There is no reason at all the current AppleTV hardware couldn't handle rentals for example if thats whats coming. I wouldn't be surprised at all to see an AppleTV firmware update, considering its currently based on 10.4.7, would be a great opportunity to move it up to being leopard 10.5 based.
Whether Apple provide the previous gen (if its replaced) with the ability is another question 😉
As an owner of the 40 gig original they better!