May anyone share an educated opinion, whether it is possible now to build/mod a real MOBA on top of Warzone? With different heroes and skills?

Yes and no. The main problem (besides the fact that it is hard and time consuming to balance everything) is that we can only have 5 different images atm. Also that kind of mod have an excessive UI which is not at all fun to make (I made the Factions mod, but the amount of time it took for the UI / saving user choices was 7/8 of the total time I've spent on that mod, and I've been working on an update for it for 3 months now)

But i am intrigued to make one, just don't expect it coming out anywhere soon xD