What i feel is,
The basic AP game with all (or a limited number) of heroes will be free to play. So you can download the game and play it with your buddies fro free.
However, for other features, you have to pay. Such as matchmaking, game modes, heroes, hats, skins, alt avatars, taunt etc. This is very similar to HoN/LoL.
The 'twist' will be a rating system (commendations anyone?) which allows users to unlock those for free or a lower price by providing some criteria to be achieved (eg: +20 leadership will give you 20% discount on a certain feature).