Apparently, after Shantae Advance, another Shantae project was in the works, called Shantae: Risky Waters. This article:

http://www.mtv.com/news/articles/1567550/flop-that-inspired-2007s-biggest-ds-games.jhtml

mentions a 13 page treatment for it being produced, and this one:

http://gonintendo.com/?p=17882

says a "Risky Waters doc" was leaked, presumably the same. I think it might be great to find it if possible, but I've no clue where to start searching.

That latter article also mentions in passing that another Risky Revolution (apparently not the same as Shantae Advance) was developed, maybe it would be cool to learn more, if there's more to be learned about it.

Edit: actually, according to the Matt Bozon interview that is almost everywhere where this info bit comes from, there were actually always Shantae projects in the works, at various stages of development, but a few are actually named or have info leaked on the net. Instead of just one page on Shantae Advance, I'd suggest maybe an entire page "Unreleased or planned Shantae sequels" summarizing the whole thing.