As far as realistic guesses go for the new belt, I think it could be useful to examine the progression of the old ones.
White: STR+1
Purple: STR+3, Haste+4%
Brown: STR+5, Haste+8%
Black: STR+7, Haste+12%, -5% PDT, +5 Subtle Blow
In terms of stats, I wouldn't be surprised if the new belt had 12%, or 16% haste. 12% if SE thinks increasing the haste even more would be broken, or 16% to coincide with the 4% increases on the preceding belts. On the same note, my money is on 9 STR to keep in line with the 2 added from purple > brown > black (or possibly 10 STR, to represent the 10th degree, since this will likely be the last belt we ever get).
All in all, my money is on something of this nature being the final product:
???? Belt: STR+10, Haste+16%, PDT(Or perhaps even DT)-10%, Subtle Blow+10,
To go with that, there could certainly be something that enhances or augments Martial Arts, h2h skill, or any other number of desirable traits. The rest is really more-so mindless speculation, but I would be legitimately shocked if the #'s for the stats I listed above deviated greatly from the final product.