to be honest i don't really like the idea. And for several reasons:
1. I really like my personla avatar, i have been using it for some years now, not only in TM, but in a lot of other games/forums too. So i really don'T want to lose it.
2. If we all have the same avatar the distinction of the players in the game becomes much more difficult. For example if someone joins the game the avatar and the nick are shown in the top corner of the game. It's a lot easier to reconise an avatar of a player, than to read his full name, especially when you are in he middle of a lap.
3. I don'T really think it would matter that much, since you never see more then one avatar at the same time in the game. In my opinion the use of unified nickcolours if far more effective.
It was once that the whole team was with the standard-colours, but as you said it has become less and less so in the last weeks. I don't really know why, i am quite happy with the orginal colours, and like to use them to be identified with the team.
So i rather would like a change there then in the avatar.