Absolutely. The choice of "Ping" for its name, rather than a more music-centric name might indicate they're keeping the door open to extend it to the whole store. (I'll add books to your list)
edit: one good reason I see to start off with music (besides the fact that it makes sense for iTunes) is that it's more common in the music industry to "follow" an artist, than it is for TV or movies. So, right from the start anybody will have people to follow while they're building their friends network.
We were just talking about this topic earlier today while speculating about a new appleTV. If all TV goes to a direct 1-to-1 streaming system, exactly how do you get people to watch new shows?
Ping seems to find that requirement exactly. Watch this get used on the TV side pretty quickly if it takes off.
I bet 'gifting' people in your Ping friends network with music (and apps, books later on) will be a profitable feature for Ping, when Apple implements it.
Funny because I meant that in the sense that simonsquiff didn't mention the books in his comment, but you're right.
When gifting right now, I don't think you have any way to know if the recipient has or not the song/app. I haven't gifted songs too much, so I'm not sure what happens in that case. Ping might be able to avoid this situation.
Gifting will do away with those Apple vouchers you can buy to the vale of 10 bucks or whatever for your friend. Instead, you can get them the song directly.
A ready-made social network, all the network infrastructure in place, users with credit cards at the ready, owned by a highly successful tech multinational....the recommendation on APPL is 'buy'!
edit: one good reason I see to start off with music (besides the fact that it makes sense for iTunes) is that it's more common in the music industry to "follow" an artist, than it is for TV or movies. So, right from the start anybody will have people to follow while they're building their friends network.