The only game i've ever seen this was in the Myth games. The setup for sins would go something like this, imagine a 1 v 1 game but with lets say 6 actual humans so 3 players per side, one player on each side is the team captain and can give control of units/planets to the other two players on the team. This would open up alot more micro as you could simply give a teammate a small fleet and he could harass an enemy focusing on nothing but his fleet while maybe the team captain is focusing on econ and the other player is given a larger fleet for full scale engagements. Possibilities would be endless like before a major engagement the team captain could give control of different parts of the fleet to the different teammates to allow for alot more micro.

A long time ago I posted this for homeworld man would it have made that multiplayer alot better and here there is sooo much more to do on a single empire that multiple people could really do alot. The way to do this is simple, if your curious, basically the team captain selects units and has a keybinding for teammates and hitting the keybinding gives control to that teammate.