Oh, this is merely assuming, but I think the whole reason behind the faction packs was to determine who wins the war.
Doubtful at best. Sets are started design on about a year or so in advance, if memory serves. It's a few months to New Phyrexia/Mirrodin Pure now. I don't know the exact timelines of sets, but I'm pretty sure it's been already handed over to Development by now, or is soon going to be, if it hasn't already been completed.
The judges had a sheet they were recording each faction wins on, which they said they had to send in, in addition to the match results.
Feature? Something similar to what they'll do for Game Day, perhaps? Just a red herring? Seriously, Action is to launch in spring. It's far too late now to decide what it's gonna be about, especially since a global theme like that decides... oh, pretty much everything about the set. Each side has mechanics associated with it. Scars had a 80-20 spread of Mirran to Phyrexian, while Besieged is 50-50. Going by symmetry and the potential names, the most likely spreads for Action are 100-0 or 80-20 in favor of either side. Since each sides has mechanics distinctly associated with it (Phyrexia has Infect, Proliferate, and various mechanics involving sacrificing stuff; Mirrodin has Battle Cry, Metalcraft, and some other non-keyword stuff), the way that spread leans has an immense impact on what the set finally looks like mechanically. In other words, they'd need to know the theme before they even start working on the set, and February is far too late to start working on a spring set.
There is, of course, the possibility that they developed both sets, and will use these to decide which of the two will be printed, but that seems unlikely - I just don't see Wizards throwing away an entire set of stuff for what is, in the end, a marketing thing, even if some or most of the cards are later salvaged. It's possible that whichever set is not printed will show up in the future, but that seems unlikely as well.