I think this would be a cool idea if they made a version of itunes, in which u subscribe and download media, that was compatible with appletv and the iphone...if this did happen movie subscription would make perfect sence for the appletv (and the iphone for that matter) and a music subsription would make sence to me at least for the iphone although downloading movies directly to the phone might not be appealing because of edge, people download songs from there phone all the time and although its only .99 a song which is the starndard for music on phones with music download capabilities this would help to justify the iphones 4 and 8GB with no apparent way to expand...
itunes users (ipod owners for the most part) are used to haveing large libraries on there ipods and the iphone is the best ipod yet and 8GB is the largest offering which is not much at all as this 8Gb also has to hadle all the phones features and extras (im assuming

) so a subscription might be an atractive offer
us spoiled ipod users dont want to constatly take songs off they paid .99 a peice for or 14.00 for the cd (9.99 on itunes) whenever something new comes out because theres not enough room which explains 30 and 80GB ipods (most people, at least that i know who have nanos or minis have libraries that reflect the size they chose and those of us with large libraries want 30 or 80 GB because we paid for them so we want to have them available all the time, at least thats how i feel) i would be much more willing to take a song off if i had a subscrition rather then buying them one by one, ... i could see apple makeing a music subscription part of the iphone plan rather then a universal option, this would make the iphone much more appealing to the 80GB ipod owners without replacing the ipod itself, (until they see how well it does possibly expanding availability in the future to appletv users and mac users) and include a version of the itunes store on the iphone, this would also open up the possibility to stream music to your phone from the store, when they move to 3g or as a wifi feature, as part of the plan which would also be a huge space saver (i.e. the appletv)
as far as movies go a universal subscription makes more sence because of the sheer size of movies...again the iphone is one of the coolest portable movie players and with a subscription you could have 1 or 2 new movies every couple of days on your iphone without paying an arm and a leg and you wouldn't fill you phone with movies...in terms the apple tv and ipod most dont watch movies over and over like they listen to music and everyone already knows that an itunes version of netflix would be awsome so no need to kill the subject....
looking into the future...i ran across an article that compares the new sandisk/yahoo sansa player against ipod and suggest that it is in fact better then the ipod and it proves many very good points
http://playlistmag.com/news/2007/04/11/sansa/index.php and if customers had the OPTION to use itunes in the same manner as its yahoo opponent it would be perfect for some future wifi enable ipods, with smaller flash memory which would help apple to retain the ipods sleek design and include wifi at the same time.... and if wifi ipod/iphone/

tv/mac users were all able to share and suggest downloads to other users like this sansa player does, you could further injure four birds with one stone, zune/smartphones/WMC/PCs, which is always good, and further promote the convergence of apple products...a subscription sounds like a good way to tie these together....it may happen it may not, .. i really don't even know if all this is even possible.... and yea jobbs is trying introduce DRM free music to itunes...but hes not getting rid of DRM altogether either

...the key is customer choice