Hotseat is really easy to add
Of course LAN is much harder
Yes, obviously changing the entire game structure to use sequential rather than simultaneous turns is a lot easier than using a different connection method for the same MP game.
Elemental turns are simultaneous, everyone goes at the same time and hitting end turn goes to the next turn for everyone. Hotseat, by definition, has only one player doing a turn at a time. So, either Elemental needs to be changed to not use simultaneous turns, or to allow one person to control multiple "players" in game. Either way, that's not in any way, shape, or form, easier than changing what acts as a server and how packets are sent for the exact same game.
The amount of effort required for that versus the number of people who'd actually play hotseat is why there is no Hotseat and probably won't be.