Really it's more a matter of it being worth it for the publishers. Right now they don't seem amenable to the idea. Remember they base the vast majority of their income on hardback sales. There is a thread here in the last few days that posted a link to a graphic detailing the very surprising revenue difference between ebook and hardback sales. I'll find it an post a link to the thread. It had some questionable data as I remember but the gist was to highlight the current differential. It's HUGE but ebooks are new and nobody has any idea where they are going in the future.
Something to ponder is it seems that in the mind of the publisher every ebook sale is a lost hardback sale. I am not certain this is true as many here buy both if it's a good book. People do collect first editions so ebooks might give publishers a chance to go back to really high quality first editions like once upon a time. But for now publishers seem to be unwilling as well as unable to move to an ebook centric business model.
I am sure avid readers would love a subscription type model. Odds are it will not be an all you can eat model as one can download all day and night. More likely it would be something like Audible where there is a monthly cost in exchange for x-credits to use as you please in the book store.
It's a nice idea but I am not sure it would be too popular in the long run since reading is very different from listening to books or watching video content.
There is a thread discussing the potential of free Kindles in exchange for some sort of subscription commitment but it's all speculation at this point.
No matter what we have to remember that publishers have a fixed overhead and their current business models have been constructed with this current model in mind. So, it is going to be years until the big publishers are able to shed some of there, often incestuous, overhead and infrastructure. So, no changes until ebooks begin to dominate sales. I send one reason for the move to agency pricing is this inability to adapt to the new market forces. Basically they are dinosaurs.
