PLAN is for the announcement to be next week. Your 2013 wildcards are (but not officially confirmed): WARD, HAMPEL, WOFFINDEN and VACULIK...
I expect the organisers will use the following reasons for their inclusion:
WARD - Invited him last year but said he wasn't ready. Has improved in 2012 so a natural choice.
HAMPEL - Certainly a World-class rider whose 2012 campaign was ruined by injury.
VACULIK - A suprising but capable rider who impressed in 2012 and clearly proved they could mix it at the top level.
WOFFINDEN - Second time round, matured as a rider and person, has improved on averages etc...
I don't expect everybody to accept the above, but, it's come from a very reliable source and of course, I work at the SGPs so pick-up on a lot of 'talk'...