I'm actually really annoyed about this, I had an original Apple TV, and the only reason I bought a new one was for TV rentals. Aside from that I see no advantage in the new Apple TV, and the lack of storage means it is in some ways a step backwards from the older models. OK, it also has AirPlay, but I am yet to have found a use for that.
So, I've now wasted my money buying a new Apple TV.
On top of that, I'm half way through renting three or four TV shows. What do I do now? Buy the remaining episodes, so that I own half of the series? buy the whole series, so there are some episodes I've then payed to rent and to purchase? It's just so frustrating.
On top of that, there are several series that I have rented in their entirety, but have done so on the selling point of rentals that you could rent three times for less than the price of puchasing once. These are shows that I will probably want to watch again, but probably not more than three times. Now, if I want to watch them again, I'll have to purchase the shows, meaning my original payment for rentals (which adds up for a whole series) was another waste of money.
So, yeah, I'm pretty annoyed at the money I've wasted buying my new Apple TV and paying for rentals which I'll now probably replace with purchases due to rentals being dropped.
I think the very least Apple could do is refund the cost of a rental for any show a user subsequently purchases, due to their sudden U-turn which had no advanced warning.