I CANNOT believe it took me this long to think about this, but it would really be fantastic to be able to sit in multiple color's seats in singleplayer mode.
I make most of my mods in singleplayer mode (as i imagine most do), and it's always annoying to have to test interactions with turns in multiplayer or to have to switch colors all the time. Ideally, we could sit in multiple seats and use the turns while playing by ourselves, with our name appearing in every seat. We'd see the content of every hand we're seated in too, and maybe the camera would spin to the new color's place when we change turns.
I bet this could even be used well for singleplayer boardgames. And it might even be a good thing to allow for multiplayer too! (as long as there's an permission we can toggle off for letting players sit in multiple seats). I could easily see this being a very useful feature for designers playtesting their board games in TTS that don't have a full player count (this is quite common).