I'll try to sum up some of my thoughts. I theorycrafted quite a bit on a simultaneous turn-based Civ-game back in 2011. I was so disappointed by Civ5 that I considered leaving my job and start making a game myself
First thing first: As you pointed out, this is
not simultaneous turns the way Civ4 and a lot of TBS does it. That's just a really bad compromise to speed up multiplayer.
Some advantages:
+ You get one model that works in both SP and MP.
+ Adding more players (humans/AI) doesn't increase time between turns.
+ You can potentially make really cool combat animations since planes, infantry, cavalry is on the move at the same time rather than the 1v1 unit fight "Archer vs Swordsman"
Main disadvantages:
- More complex and difficult rules. There's a lot of situation where its not clear what will happen. Here's just a few of the most obvious scenarios, do these units fight or not?
- Clarity on the map. You need to show where a unit is ordered to move. This can become a mess on the map.
- Less precise feedback. When you order a unit to attack in sequential turns you get the result immediately. This seems very minor, but its all about the feeling of satisfaction for the player
- Even though you don't have "time between turns" in the sense that you wait for other players to finish, you still need to show where units moved etc. This makes the player sit idle, often for longer than what just waiting for the AI to take its turn would have.
Then there's quite a few neutral differences. Simultaneous turns offer a less clear gamestate. You need to think "what will the other player(s) do?" on a whole different level.
To me the crucial point is that you need to succeed in making the resolve phase engaging and fun to watch. It also needs to be 100% clear what happened so it doesn't feel like some random stuff the player can't control.