I don't see a lot of major game companies investing into touhou. There are very few choices.
Nintendo was brought up, but I don't see it happening. Nintendo has a wide range of games, but none of them are particularly japan-o-centric. Pretty much all of Nintendo's IPs are very conservative as far as nationality goes, perhaps Pokemon is the one you'd associate the most with Japan considering the anime behind it. Touhou is very much a widget series, it doesn't fit Big N's style.
NIS makes very widget games, but they primarially make only RPGs. Also, they only really have original IPs, so I don't see them taking Touhou
Atlus sounds like a good choice at first, until you realize they primarily publish games, not develop them. Even if Atlus acquired it, they would only really license it to another studio to develop.
If we're only talking large game companies, my bet goes on SEGA or Square Enix. Both are huge and not afraid to pander only to Japanese audiences with some of their studios. Of course, it'd still be Japan only, and the gameplay would probably be radically altered, but it would work. SE in particular has a business model that goes hand in hand with the content Touhou puts out. Offical music CDs, books, anime, games, merchandise, Square Enix loves to go all out with their products and sell it in every possible manner.
...But actually, I think Touhou is more likely to be picked up by an anime studio. The games are super niche, but the fleshed-out characters and world design would make for a killer app in the animation industry. A Touhou anime would finally make the series mainstream, and the game side of the equation would easily either be dropped, retooled, or licensed out to a smaller company, the latter most option most likely to spawn more games very much still in style with how ZUN makes it. Maybe they'd just give the license to Tasofro to just make more Touhou games.