The third set in Scars of Mirrodin block is code named "Action", following the prior two sets being called "Lights" and "Camera" respectively. Normally, WOTC would have revealed the name of this set, but in an effort to keep people guessing the outcome of the war, they have registered two names.
The outcome is decided and thus far WOTC have kept a lid on things. I believe that the winner is easily deduced though.
My reasoning is multi-faceted. If the third set is Phyrexian based, it allows them to add infect to Red, a colour which has very few Phyrexian cards. This would also justify the Mirrans needing to make the final sword in the Sword of X and Y cycle, as this would have to be protection from Red and White. It would be a tool crafted by the Mirran resistance. It's possible that the Phyrexians could make it, but that would bring it out of sync with the rest of the cycle, which is Mirran made.
In the players guide, available in the Mirrodin Beseiged Fat Pack, they talk about the 5 Phyrexian Praetors. Each one is aligned with a colour, which means we haven't really seen what the Red one is up to yet. Also, the images of each is done in silhouette. This means they are likely to be revealed in the next set. I feel this makes more sense if they are the winners. It sets up things to deal with a five faction civil war in the wake of their victory.
The Mirrodin Beseiged Game Day has two Faction promos available. Both appear in the next set, but as promos are aligned with the two different set choices. Suture Priest has the set symbol for New Phyrexia and I feel makes more sense in that set. While it could be a straggler on the way to Phyrexia's defeat, it makes more sense setting up the religious overtones of the White Phyrexian faction, which lead to that faction coming to blows with the other five. Pristine Talisman however, has the set symbol for Mirrodin Pure. I feel the name gives things away. It is more remarkable for the talsiman to be pristine, if the rest of the world has fallen prey to Phyrexia's corruption. This gives more credence to the idea that in the wake of Phyrexian victory, the Mirrans will set up a resistance movement.
It will probably take advantage of the Phyrexian civil war and lead to a story for another block. The final set of that block could easily be called Mirrodin Pure, as WOTC would still have the trademark. The Mirrans reclaiming their home would take a long time, so would be perfect to re-visit further down the road.
Another idea for a future block could be a return to events similar to the Phyrexian invasion of Dominaria. Possibly even repeating their efforts, which would open up a block to return to that plane. While this might seem like repeating story ideas, Maro has often said things work in cycles, and it's not hard to believe that the Phyrexian's would return to finish the work Yawgmoth started. Given that he might not even be dead, this would lead to more interesting stories.
Finally, it would be a shame for the Phyrexians to return, only to be dealt with in the space of one block. They were the villains for such a long time that it would be nice for them to return to prominence. It also gives Nicol Bolas a break from being the villainous focus, while continuing to allow him to work from behind the scenes. Also, the Eldrazi were around for one set, if they were defeated then they were not the threat they seemed.
That's my reasoning. There is evidence to support my theories, as well as compelling future story reasons for the war to go that way. Guess we will find out if I'm right when the set comes out.