My money is on the 20th.
As far as what we will see, my guess is little in the way of math changes, probably just a few concept updates. The biggest and most key thing being multiclassing...as we haven't seen it at all yet.
Mearls specifically mentioned the next packet is the big math change (that many are clamouring for).
...the "math" argument has been hilarious...
I haven't followed... what exactly is the "big math change" wanted?
In addition to what Weather Report says above, the idea was supposed to be that DCs of spells would again scale as you went up levels. Since DCs would scale, saves would have to scale to match them. Plus, there was a desire to make skill checks get easier for higher level characters, thus a scaling check modifier.I haven't followed... what exactly is the "big math change" wanted?
In addition to what Weather Report says above, the idea was supposed to be that DCs of spells would again scale as you went up levels.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.