In Heroes 5 online, simultaneous turns are used, but they last until the first possible contact (if any hero is within 1 turn's distance moving toward the opponent (taking into account the opponent's move in the opposite direction) - it instantly switches to turn-based mode ... from my own experience, I played simultaneously from 112 to 211.
The only difficulty is that in Heroes 5, dimensional gates are used a maximum of 2 times per turn (taking up half a turn), and for a distance that never exceeds the length of a hero's normal move, whereas in Heroes 3 this is more problematic.
Respect to asm. I would like to see specifically an improved SoD, diluted by no more than TE-lite.