Here are some of the details that we are going to see in the next book.
ReConquest Phase 2
-No new faction this time around. Those that have followed this game for awhile already know this, but a new faction is likely when we see the third and final Reconquest phase 3.
-extreme weather rules. That's right, snow/Ice, underground, and other heavy weather effects, including battles at night.
-a new infestation mechanic with free roaming beasts or other monstrosities that can damage even the strongest of tanks.
-the new standard commander units will have their rules in the new book.
-rules for the three new infantry/small vehicles that have not yet been released (first ones get released next month).
-at least one new unit for each faction that has not yet been finalized (and I couldn't get more info on)
-new scenery rules, like for the underground hanger. I expect we will see experimental rules still before this. Yes, I asked for hints.... but none as of yet.
If you want to know some of the details of what the infantry releases will be like, we had those some time ago. Here is a link.