That's Right! ZUN has announced it on his blog!
You can see it here:
http://kourindou.exblog.jp/14332117/It's called Touhou: Toushinrei~Ten Desires.
It stars Reimu, Marisa and Sanae as the returning Playable characters, As well as one more player, Youmu Konpaku.
Check it out!
From Zun's Blog:
"Basically, the story is "Suddenly a large number of spirits appear - the type that are called divine spirits! A young girl appears to investigate, knowing this can't be left unchecked."
The main characters include Reimu and Marisa as usual, as well as Sanae, who's trying to learn to use divine spirits effectively, and Youmu, who's here to deal with any divine spirits that aren't under her control."
