Actually, Spanish is my born language and I can say for sure that the article DON'T says that Mercury Steam will make the 3DS Castlevania. It only speaks about the DLC and "Lord of Shadows 2" (things that we already know) and, then, that there will be a Castlevania for Nintendo 3DS. But actually, it isn't from a reliable web page either.
I don't think that hire MS for the 3DS Castlevania would be a good idea. They should keep the team for the "Big" games. But, actually, I really, really, really hope that IGA will get fired pretty soon. Please, don't let him make unlimited sequels "Ass of sorrow" sequels...