Quoting Rhonin_the_wizard, reply 11
Hotseat is a local form of multiplayer, where each player takes their turn playing the game on the same device. I don't know what StarDock means by asynchronous so I can't answer that.
I don't know what Stardock has in mind specifically, but asynchronous multiplayer is any method where players don't have to be playing at the same time. Play By E-Mail (PBEM, mentioned earlier in the thread) is probably the oldest method for video games, with chess games by mail being older than that.
That works by me taking my turn whenever I want, then the game sending you an email saying it's your turn. At some point you take your turn, then the game sends me an email saying its my turn. This keeps going, with us taking our turns whenever we feel like it. Games last a VERY long time, but you can play with someone even if your schedules have no overlap whatsoever. Turn based games are well suited to it.
Civ IV & V have the Pitboss system to coordinate it. Pitboss is a server that sits somewhere and manages the game, letting players take their turns and optionally sending out notifications when it's your turn. You can play games with several players using this system.
Hotseat isn't asynchronous, as everyone has to be in the same location at more or less the same time. (Bathroom breaks don't disrupt other players of course.)
End of Tridus's quote
Hot seat is just a faster version of asynchronous played on the same machine. I've played PTO II hot seat where games took a couple weeks, even with the two players in the same room. That was on Super Nintendo, so PBEM was clearly out of the question. In fact, at one point we'd play two games at once - I do my turn on game 1 while my brother was doing his turn on game 2, then switch. THAT took a bit of mental agility to keep what you were doing in each game separate.
I could see a huge benefit to switching between the two modes in the same game, though. Start a game with several people playing hot seat; when the night ends you continue playing (at a much slower pace) over PBEM; then the next week or whatever when you get together again you could resume hot seat at the much faster pace.
It may not even take that much to program, if Stardock is using Steam to run whatever asynchronous mode they already have planned. Players may even be able to fake hot seat; have Player 1 do his turn, log out, have Player 2 log in to the system and do his turn, log out, have Player 3 log in and do his turn, etc. It would get tedious logging in and out all the time, but it could probably be done. But if Stardock adopted that sort of thing, addressing the log in/log out tedium could be a user interface issue rather than a program-a-whole-game-mode-from-scratch issue. It would require Steam to be in online mode to make it work, though, since you'd essentially be playing a PBEM system with every player using the same computer sequentially.