Time Warner picking up Acti-Blizz I don't think would change the playing field all that much. Time Warner has been making incremental studio purchases for awhile and their success has been decent with the whole Batman line. Nothing stellar. Picking up Acti-Blizz would make them a major player obviously.
Microsoft picking up Acti-Blizz has a lot more interesting potential. Although they might remain their own distinct element for a couple of years and just be business as usual, the possibilities that could arise from them acquiring Acti-Blizz's IPs are endless. Exclusivity is always in question but I would be curious to see if B.Net got merged with XBL in some fashion or a new spawn service would be born.
Not saying any of this would be better or worst. Just interesting.