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

I think it's an interesting idea... Have the developers already described the Rukh birds in Ashan? If not, then it could definitely be added. Suggestion: not as birds of thunder (this is an idea from the third game, quite unique), but as those very birds with iron feathers from myths, perhaps as bird-golems. Like a living airplane. Well, it's up to you in any case.