If Apple uses the exact same enclosure for the 2012 Mac Mini's, then you can expect again that the max TDP between the processor and GPU needs to stay at or under 45 watts. In the server mini of 2011, Apple chose a 45 watt TDP processor and didn't pair it with a discrete GPU. However, in the mid-mini, Apple choose a 35 watt TDP chip and paired with with a relatively medocre GPU. Unfortunately I can't find the TDP of the 6630 but I'm assuming it is at or around 10 watts TDB based on a table on this page:
http://en.wikipedia.org/wiki/Comparison_of_AMD_graphics_processing_units#Radeon_HD_6xxxM_Series (Other entry level 500/800mhz GPU's are using around 7 TDP so assuming that the 6630 released a bit more heat due to being a more powerful over all GPU, I think it is safe to assume it uses roughly 10 watts). That again brings the TDP total to roughly 45 watts TDP between the GPU and processor.
Based on the info provided by philipma, I think we can safely assume that any discrete GPU based Mac Mini will probably use either the Core i5-3320M or Core i5-3360M with a "high end option" of the Core i7-3520M. I don't forsee Apple using the low power Core i5-3427U or Core i7-3667U in order to cram a faster GPU into their next Mac Mini's. Something tells me they will reserve those only for their Macbook Airs.
What GPU they will include is a tough one, maybe the AMD 7730M or the 7750M? Or maybe Nvidia? I am not sure what the TDP ratings on the above GPU's are so it's hard to say and it also depends on the benchmarks of the Intell HD4000. It may be that the 7730M isn't all that much faster than the HD4000 (who really knows and I haven't gone looking for benchmarks yet). If there isn't any value added by going with a medocre discrete GPU vs the HD4000, maybe Apple will drop the discrete Mac Mini altogether. Until the 2011 Mac Mini's, apple hadn't had a discrete GPU in the Mac Mini since the G4 days...