Wesnoth at the core is a sequential game, not a simultaneous game. FreeCiv is already a simultaneous game. What if all of Wesnoth's assets and rules were ported over to FreeCiv's engine with some modifications like a unit attack priority to smooth over combat.
https://policonomics.com/simultaneous-game/
https://policonomics.com/sequential-game/
Battle For Wesnoth modpack
Re: Battle For Wesnoth modpack
There is lot of incompatibilitie between Freeciv and B4W. Mainly, FC allows any number of units per tile that makes very different warfare. Then, Wesnoth units may have individual terrain speeds when Freeciv unit either can enter terrain or can not and there are only 3 possible speed modes 2 of which are terrain independent. Also, experience system in Freeciv is random scale of bonuses, not experience-evolve model (this one might be fixed in v.3.1 though)... Really, it's more likely one just forks Wesnoth for server with simultaneous moves. I don't know its code well, maybe it's even somehow possible in standard application, or is already done.
Re: Battle For Wesnoth modpack
Iris on Wesnoth's discord server says the Wesnoth's engine was designed so that only one player could play at a time. I would guess it would have to do with locking. I doubt changing locking is as easy as modifying some interactions and importing some textures and music. I don't really know either.