Captains Mode role selection.

A "role draft" gamemode might be fun to play, but implementing it in the captains mode would be a real shame: I'm thinking about an all pick gamemode with a smaller Hero pool depending on the role you want, pretty convenient for when you want to solo queue. As the others say, though, there are Heroes that can fulfill multiple roles, so the Hero selection might end up being inaccurate; but who said a specific Hero can't be selectable for both the support and the carry role?

Another problem is that defining five roles isn't very easy, as there are many ways to build a team: "carry" "support" and "initiator" aren't always what a team consists of, same for "ganker" or "jungler". I think it would be better to relegate a Hero according to their farm priority: "1" would be safe lane carries, "2" would be mids, "3" would be both carries (for when you want to play an aggressive trilane) and off-laners, "4" and "5" would be all the supports including Mirana, Naga Siren, Sven and the other unusual supports.

I agree with Peppo, farm priority is probably the best way to divide roles, because of the large amount of different "roles" there are for the same heroes. For example Alchemist, Naga and Mirana can play almost any "Role". That is what's great about Dota, the diversity of the roles each hero can take.

I think a role indicator is a really good idea. Much like placing your icon on the minimap, it would be helpful to indicate how you intend to play the hero.