Rentals would certainly help in the US. The Apple TV is already dead everywhere else though.
I was interested in the idea when it was announced, thought it had the idea to change the way people watched TV. I haven't given it a second thought since. For me there is a single overriding issue: Whether the functionality changes of not they can't hide the fact that there is currently no content for it.
I get DVD's in the mail from Zip (Canadian netflix). Its much easier to watch those on a DVD player than it is to try and get it onto an Apple TV.
License agreements prevent me from buying or renting any content from iTunes, so that's non-starter.
I don't see enough worthwhile content on YouTube to justify a $349 dedicated YouTube playing box.
Likewise for Video podcasts.
As for streaming music
Wii Transfer already streams iTunes playlists for me, without adding an extra box.
The only thing that can change this is rentals that offer a better value deal than the $24.95 / month subscription I get in the mail.
Since they can't even sell me a Pixar movie yet, I don't see that happening anytime soon.