Argh, correction to something I previously said. Suika's win quote to Yukari about Nirvana was actually a win quote to Yuyuko, not Yukari. When I'm really sleepy at night, eye sight becomes blurry and the two names look the same. That said, I still personally feel the same way about Yukari's current goals after re-viewing her SWR ending.
The End of Yukari's SWR Ending:
Then again, Yukari seems to be saying to Suika in her win quote to Suika in Hisou Tensokou that she thinks Suika would be a better god than those "clumsy gods". Maybe that means something, or maybe it doesn't.
"i are quite impressive, and quite popular.
Have you perhaps gathered more faith than the clumsy gods? " ~Yukari to Suika, Hisou Tensokou
Of course, as with all future plot speculation, I can not say for certain that I'm right.
...alright, what can I say? I'm a glutton for punishment, which I suppose is partially why I made this thread in the first place. So... my findings on whether or not Suwako could/should/would have been a human before.
http://en.wikipedia.org/wiki/KamiAs we all know, a lot of the Touhouverse is heavily based on Shinto stories/whatever. The main protagonist, Reimu, is a Shinto shrine maiden, for crying out loud, and even the entrance to the Netherworld that Maribel saw was a shinto gate. Sanae, too, is obviously a shinto shrine maiden. As you can clearly see in the link, both gods that are the deified personifications of things such as the wind (of which Kanako obviously is) and humans that become deified enough to be gods (like Mizue) all fall under the same category of shinto god (Kami). Thus, logically speaking, they PROBABLY fall that way within the Touhouverse, too. ZUN isn't forced to abide by what the legends say exactly, but it's very clear that he bases things heavily after them when he can, so I guess you can say that if you had to bet on one thing (that Mizue and Kanako are the same type of god, which matches Shinto belief) or the other (that they're two different types of god), odds lean towards the former than the latter. Of course, we don't have any 100% confirmation here, so in the end, there can't be any clear winner in this debate, but I think I'll stick with the odds for now.
Anyways, fortunately, there is one thing that certainly IS clear. Sanae is officially a living god NOT because she's a demi-god and NOT because she's Suwako's descendant (well, not directly because of it), but simply because people had so much faith in her that she became deified.
http://touhou.wikia.com/wiki/Sanae"In addition, as keepers of secrets, they began to accrue faith and be treated as gods, even though they were humans. They became living gods. " ~Sanae's MoF profile
So basically, Sanae BECAME a "living god" because of faith in her. She wasn't born as one.
(although as it is, "living god" seems to be more just a figure of speech since Sanae continues to be referred to as a human in most other cases)
Sanae:Today, you won't be getting away!
I may be only human, but nevertheless, I'll have you regard my convictions!
Suwako: But Sanaeee,
you're not a human, you're a living god, a miracle-worker...
Sanae: All the better, then.
I can stand equally with you!
Sadly, there's a decent chance something is being lost in the translation here, but I'm pretty sure Suwako is sarcastically mocking Sanae here with "Only human? Everyone calls you a living god, remember?" (and Sanae of course just runs with it). By itself, the conversation could have multiple interpretations, but at the very end of everything, Suwako taunts Sanae with this:
Suwako: Well, then! Awe me, creator of these lands,
with your marvelous, god-like miracles!
Considering that it's Suwako herself that's actually been a creator of lands of sorts (in MoF, she tells both Marisa and Reimu, "Simply admirable for a human to defeat a god who's built up a country by herself. ") and that she's saying Sanae's miracles aren't god miracles but are merely god-like, she's basically just saying that Sanae's "living god" status means nothing (of course, something like this naturally comes with the subtext that if Sanae really wants to be a real god, she's going to have to prove herself. Suwako WANTS Sanae to get stronger, after all)
Side note: Misue too was a living god for a bit according to Cage in Runegate Chapter 3, but stopped being one after he... er, well, stopped living (I mean, he died. Obviously). After that, he became deified, which is pretty much how a human becomes a kami according to the wikipedia article.
Remilia seems to do the same type of mockery that Suwako is doing to Sanae, too, except more explicitly and without the "Prove it!" subtext.
"Heh, so only causing wind to blow makes you a god?" ~Remilia's Hisoutenko win quote to Sanae
And this quote from Hatate in Double Spoiler calls Sanae a human.
"She's the new miko on the mountain. She's a human but seems like a god.
I wonder what's the difference between a god and human. The taste of their meat?" ~Hatate
...how confusing. I imagine something's just lost in the translation when it comes to all of this.
Still, because Sanae is only a living god thanks to people's faith in her, it's arguable that her miracle powers by themselves aren't god-based at all (and thus, quite possible for her to inherit them from a human Suwako. The other abilities from Suwako that she needs to actually borrow from Suwako and Kanako to create those miracles, however, are truly god-ish, but using them via the miracles themselves is merely "god-like." )
However, I only said it's arguable. Not 100% certain.
"The ancestors of a particular family can also be worshipped as kami. In this sense, these kami were worshipped not because of their godly powers, but because of a distinct quality or value. These kami were regional and many shrines (hokora) have been built in their honour. In many cases, people who once lived can thus be deified as gods; an example of this is Tenjin, who was Sugawara no Michizane (845-903) in life.
" ~Wikipedia on Shinto Gods, Kami
While researching this, I also came across a quote which might have relevance to the touhou logic thing.
"All mythological creatures of the Japanese cultural tradition, of the Buddhistic tradition, Christian God, Hindu gods, Islamic Allah, various angels and demons of all faiths among others are considered Kami for the purpose of Shinto faith." ~Wikipedia article on Shinto
Note, however, that while all the above are considered Kami, "Greek Gods" were not included. On the other hand, if we assume this wikipedia statement to be true at its most literal form, that would mean all Youkai are gods, too, and that's just silly and wrong.
Still, this quote from Suwako seems to imply that even a human made into a god by faith is the same type of god as Suwako. Otherwise, she would have differentiated it somehow (in the quote's case, she's talking about how a bat can become a god)
"There also exist people who believe in bats as good omens.
However even with such trivial amounts of faith, one could become a god, right?" ~Suwako's win quote to Remilia in Hisou
I did stumble across this win quote from Komachi to Suwako that implies at least Komachi thinks Suwako (and Kanako) were human once, since they had to transcend the cycle of rebirth. Either that or gods too are subject to the cycle of rebirth and need to reach Nirvana, themselves, but that sounds kinda... odd. Maybe something's being lost in the translation here.
"In the stages of life and rebirth, both of you can be seen as Gods who've completely transcended the cycle of suffering. Is that right? " ~Komachi to Suwako
And this is the line that probably led to me accidentally thinking Suwako was officially confirmed to be a human earlier in the first place. I must have been too sleep deprived at the time (since it's a win quote to Sanae, not Suwako)
"You should be aware that before you were a god, you were a mere human. " ~Tenshi to Sanae, Hisou Tensoko
Finally, in the end, after lots of searching, I couldn't find any case of a shinto god giving birth to a mortal with the exception of the Imperial Family claiming they were descended from the highest god, Ameraterasu (which was so the emperor could/would be worshipped as a god, himself). However, in 1945 (World War II's result), the emperor disavowed all divine heritage and polytheistic heritage worship was no longer permitted. That is the only case I could find of mortal ancestry from a god (and I'm not sure that even counts, since the emperor claimed to be a god, not a mortal. ...and then the emperor disavowed deity heritage after WWII, and ZUN is clearly aware of WWII's ending because at least one Touhou win quote was a reference to Japan's military strategy after WWII. So... hell if I know how that would apply to the Touhouverse). Also, the Emperor obviously didn't inherit any of Ameratsu's sun powers whatsoever.
...I didn't search through every Japanese God though. Because good grief, there's a truckton of them O_o
My final verdict: ....honestly, at this point I don't care anymore. There isn't enough actual in-game confirmation of various things to even begin to come to a conclusion that isn't speculation. And that includes refuting the possiblity of Suwaka ever being human in the first place.