For individual studios it's Certain Affinity, IOI, Asobo, Platinum Games that i would MS to target a dark horse pick of mine would be Pearl Abyss or Crytek, once again I will say that if MS were to go for a Japanese publisher it needs to be Capcom. My scenario would be that Sony triggers a Square Enix acquisition and then MS triggers a Capcom acquisition at the same time then Sony wouldn't be able to complain without the FTC, CMA, EU looking like hypocrites.
It also really sucks that they lost out on Crystal Dynamics and Eidos Montreal due to this deal though.