It is going to be optional which is good.

Some games are difficult to give a demo of because it's all or nothing.

Plus adding in IAP and demoifying a game can be a right royal pain in the bum - especially when you end up making about one or two sales then wonder why you even bothered.

My Android games have sold plenty of copies without having a demo version (and got good ratings on the Google Play store, not buyers remorse) but the free to play style versions here have not earned me a penny yet - as I obviously haven't hit the amount you need on OUYA to trigger a payment being sent out.