Heroes 6 - Discussion

On one forum, there was even a serious suggestion that the 5th faction could be Nagas, who are neutral in their beliefs, and the symmetry would be preserved. But no matter how you look at it, Mages and Elves are traditionally good, and it's unlikely that will change.

Then yes, Elves/Mages and Nagas. The symmetry is preserved until the first expansion with new factions. Although I have vague doubts that the developers will mix standard factions and be happy about it...
Regarding the neutrality of the Elves, after Adepts, they fit perfectly into this role.