What is your opinion on the possibility of introducing a third tier of maps and a new faction into the game?

The third level might be met with resistance simply because it's unfamiliar (as is any innovation). Some might feel that it doesn't fit with the established traditions of the game, but, as Andrey said (and I agree), we've already introduced dungeons into the game!

No, the third level isn't needed to expand the map's area. Although it will be useful for that too.

Personally, I'm only concerned about one thing (which has already been mentioned): the proposed underwater exploration... It's easy to connect it to the surface and the dungeon. But it's more complicated with the heroes. How do you envision this? Are they going to wear scuba gear? If we create a third level, we need to consider the possibility of communication for all factions.

We should focus on the "surface-dungeon" concept.