Their history with acquisitions is pretty poor and they've certainly dropped off from doing it regularly. The 5 most recent ones are Mojang, PressPlay, Twisted Pixel, BigPark and Lionhead (dating that far back).
LH were in bad financial difficulties, I think PressPlay were going that way and were already working with MS on Max and wanted to not have to worry about doing contract work, TP I'm unsure about, BigPark was Don Mattricks baby before he went to MS and Mojang was for Minecraft.
Taking out BP and Mojang it seems to me considering the long list of other studios that have gone elsewhere in the past (Double Helix, RedLynx etc) I think unless a studio is in trouble of money issues MS won't really dip in and buy them.
I would love it if MS bought Remedy and Playground personally, but I suspect neither of them want them to be bought. Im not expecting any other studio acquisitions either