Seems like a good idea, probably something Evolve should have done. I'm very much a supporter of free 2 play now when its done correctly, loving the Heroes of the Storm beta right now, which has this character rotation thing, i even put a few £ in to buy some characters.

People need to just get there head around free to play, if you played one for about 10 hours plus, surely that amount of entertainment might be worth you throwing a bit of money in to unlock some of your favourite characters permanently.

Edit:

So far ive put about £30 into hearthstone with the Naxx expansion and 15 packs on the GvG expansion was released. But i must be close to 100 hours played now, 100 hours of entertainment for £30 is a bargain. 

Good news, now people will stop hating on F2P like Deep Down or Drawn To Death

you have too much faith in the humanity of others..

Indeed. Gaming needs to expand into new ways to entertain, and I am happy Microsoft is doing a great contribution towards the evolution. Granted, F2P hasn't reached its full potential, but with measures like this, it will become one step closer.

This game has a bit of PvP (with one player controlling the dungeo nmaster, correct me if I'm wrong) and that has a dangerous possibility to be P2W. It does not sound like it will be that way so that's good news, but we will see how this is handled. Did MS have no faith on this game or something that it went F2P?

i dont think it has a p2w thing  since say the dungon master buys the most expensive powerful monster he can chances are then that will be the only monster he will be able to put on the feild.  since i belive every map or mission (dont know havnt played the game) has a set number you can place