Are we going to see a fundamental change in game mechanics, or just plot? Because I'm just trying to start up a new Dark Elf army and will be a little pissed if suddenly the entire army becomes invalid...
The amalgum of rumours seem to point to:
Combined armies ala End Times (So your DE should be as fine as my WoC, but will eventually be part of a larger Elf faction, same with Chaos, and forces of Order in one iteration or another.)
multiple modes of play, one is a skirmish game called Age of Sigmar, and another seems to be very similar to 8th ed.