ShinyCharizard said:
I'd like them to make an open world rpg with combat mechanics similar to Bayonetta. [...] Also Darksiders.
Pretty much this. Darksiders would be brilliant in their hands and is pretty much the best thing that could happen to it at this point. Platinum may very well make a better Darksiders than Vigil did.
And the style of action combat that Platinum does so well is the best type of combat of any genre, so adding it in to any game with action style combat would be great, especially RPGs.
It would be cool to see them take over the DMC franchise too, but I think Itsuno and his team at Capcom are more than capable of handling that, if Capcom would just let him. Plus, Platinum already has Bayonetta, which is in many ways just DMC but with a woman, and quite possibly Metal Gear Rising. Three action game franchises from one studio is kind of overkill.
Seeing them collaborate with Grasshopper could be really amazing too. They have similar sensibilities in style and tone, but Platinum seem to have better production values when it comes to gameplay. Suda51's mad genius combined with Platinum's excellence in the same type of games could create something really special.