RTF is a global modification that replaces all towns in the game.

I can assume that only hero Dark Guardians will have such a model?

Yes, there will also be a model for the hero of the Wind Swords and possibly mages on Arantir, but they will be very similar to elementalists, although elementals may get heroes on flying carpets.

In general, a gnome and a dark elf from the cities of Leafmore and the Eridan Crossing are also planned, and they will also get models.