2013 is hopefully becoming less of a mystery as we approach the end of 2012. According to this schedule, which conforms to what we have been hearing from Hastings and other rumor mongers, Dark Angels are up next, followed by Daemons, Tau, and Eldar later in the year.
Please remember that these are rumors. Salt is always required.
via Larry Vela over on Bols
JAN: Dark Angels
MAR: Wave month (hobbit, warriors of chaos, 40k)
APR: High Elves
JUN: Summer wave (40k, supplement book for 40k)
AUG: Mystery Box
SEP: Wave month
Now, as usual, these things tend to get more speculative as you go outwards in time, but overall these line up with what we've been hearing from a variety of chatter. We've been hearing for a while that the "Mystery Box" is a fully revamped Blood Bowl. This list would certainly be a "year of xenos"