Since it's all conjecture at this point, I'd look at the FX8 for an indication of the block instance quantities per preset available on AX8. That is, two each of the blocks that makes sense (delay, reverb, drive, EQ, etc) and one each of the other blocks (multidelay, enhancer, etc).
All we know for sure is 1 amp / 1 cab.
I read on a TGP thread somewhere that AX8 might only have 1 reverb instance, but I think that was a misinterpretation of Joe's comments in a video.
Cliff and Co mentioned that 4 drives for the FX8 could be a possibility. That'd be cool.