Heroes 6 - Discussion

it's enough to capture cities (by the way, when occupied, they can be turned into settlements of your race)

Such a feature was already implemented in In the Wake of Gods... The idea itself is good, but it shouldn't be overused. It can be included somewhere in the campaigns where it is needed for the plot, but in multiplayer it is unnecessary. By the way, rebuilding a city in In the Wake of Gods is not easy:

including gremlins, kobolds, trolls, and gnolls.

Yes, there were no kobolds; they seem to have mixed something up here:
I looked at the picture of the battle between two armies, and there is something hovering above the necromancer's army that resembles a gargoyle from that "we need to build a ziggurat" :D So, perhaps, there will be impressive gargoyles, but in the necromancer's army. And for the mages, they will be replaced by harpies or something else exotic...