Jesus, that's horrifying. It's like something out of a messed up doujin or something.
Actually, that's from IM. I wish I was joking.
We can already see her getting nerfed by ZUN in SSiB.
Yes, at least as far as her gap travelling is concerned. She can only reach the Moon once a month and only by opening a boundary on the surface of the lake. And even then she only reaches the near side of the Moon, which is the exact opposite where the Lunar Capital lies. Likewise, in SWR, it took her several "gaps" to reach Heaven, though that could have been intentional.
As for her battle abilities, we can't really say she was nerfed in SSiB as she did no actual fighting. She could have just been acting inferior as a decoy, so that Yuyuko would have enough time to do her job. And she's been known to lie and deceive on many occasions. Telling a few lies to her shikigami would not surprise me. She also seems to fear/have a great respect for Eiki Shiki, as shown in Seasonal Dream Vision, though that can be interpreted as simply not willing to listen to/argue with her. Even when there are characters more poweful than Yukari, she is smart enough to know who she can and cannot handle. Someone like Remilia or Yuuka, who are so confident about themselves, would probably want to challenge the Watatsukis head on just to see if they're as strong as they say. Another limitation of Yukari's power could be shown in PCB backstory, when instead of sealing off or destroying Saigyou Ayakashi, she uses Yuyuko's body as a seal and send the tree to the Netherworld.
While boundary manipulation would technically allow her to manipulate everything, she is not omnipotent. Therfore, I think that ZUN defined some characters' abilities incorrectly.
For example if Flandre could really destroy "anything and everything" as her ability is defined, she could destroy, not only objects. She could destroy concepts. Reality, void, she could destroy water, the sun, a meaning of a word, herself, a God, the concept of immortality or time itself. But she can only destroy things that have an "eye" which she can crush. That alone already subtracts quite a lot of things from the "anything and everything" group, meaning the definition is not true.
The same could be said about Yoshika. With a bit of stretch, she could be able to copycat Keine's ability and "eat" history. Or she could consume someone's memory. Or knowledge. Giving the cheesy zombie line: "Braaaains~" a whole new meaning.
Or Seiga's ability could be extended as being able to pass through the walls of reality. And she'd be able to do the same thing that Reimu can, using a different concept.
A lot of the so called "broken" powers in Touhou have some sort of limitations, and in a world where Spell Card Rules apply, they hold no meaning anyway. And a lot of these powers are not well defined by ZUN.
So, this is for your fanfic, isn't it?
Well, yes. I was under the impression that this thread exists to discuss writing ideas.