Age of Empres 2 has a neat but rarely used feature that allowed two players to control one team.  It was rarely used because the size of AoE2 was limited and 1 team with 2 players was still inferior to 2 teams with 1 player.

With the size of soase though, two players on one team could really be put to good use.  This would especially be the case on multi-star games, as a lot of those battles can be massive.  I really enjoy playing with friends this way and on AoE2 we were always stepping on each other's toes due to the small sizes.  I think this is something that would work well with Sins, although it's still true that 2 teams will be better than 1.  That fact really won't matter though, if people are having fun with it and working well together.