Will subscription-based music services trump iTunes?

This question was a hot topic at the Music 2.0 conference in L.A. this week. Everyone from record labels to online retailers is gushing over Apple's success – and predicting its demise.

The strongest argument in favor of subscription-based services is that they provide access to a greater variety of tracks and artists for a low monthly fee. While this may be true, the major drawback remains portability – you can stream as much music as you want from your Mac (*if* the services even decide to support us!), but your subscription is useless when in your car, out on the town, or anywhere that is not right on front of your computer.

What do you think – will the iTMS ever gravitate towards a subscription-based model? Will subscription services begin taking market share away from the iTMS? It seems to me there is likely room the growing market of digital downloads for both approaches. Perhaps Apple could take advantage of both worlds, and offer a subscription service in addition to its standard a la carte downloads. I know I would sign up.