I voted for Novgorod, TO and Scotland. I think all of the civs should be included, but that needs RFCE 2.0 working.
All African civs should be included (lots of Free Space, counter or vassals to Ottomans). Denmark and Norway may wait (but rethinking their UHVs might be needed, if we want the Norse to be played further).
Aragon, Sicily and Tunisia are nice to add, but the three added together might break the balance, and make all 3 easy targets for their hungry neighbors (Spain, Genoa and Morocco).
So my votes were for the 3 I wanted
first:
TO/Prussia has already been largely debated, so adding it would please all who have been researching and debating about it, and the material we already have is at least bigger then everyone else.
Novgorod is a must IMO, lots of empty space and a counter to Muscovy (as it really needs one). And that Nevsky LH will fit perfectly as...... Nevsky

.
Scotland will counter England (or finally make it become Super England), the only nation in RFCE that keeps losing 1/4 - 1/3 of its own territory over and over again to that minor revolution mechanic. Once I've seen Germany taking Scotland because England wasn't fast enough to reconquer it (I think they might get tired). Actually in most of my late games, Europe is battling Europe, and England says it's part of someone's alliance, but in truth it's just waiting for the next Scottish rebellion.
And I hope that after the inclusion of Novgorod, an earlier Sweden and the Crimean Khanate, we may start thinking on those Eastern Steppe Colonies to give the Eastern powers a chance of competing for more space out of Europe (instead of awarding Muscovy all the goodies concentrated in its eastern border).