As someone who signed up for HBO Now and Pandora through Google's Play service in exactly this manner, I imagine this is the reason they are adding it. It's very easy. The one downside I encountered is that when my card changed and billing failed, it automatically unsubscribed me after what appeared to be a single failure, and I had to sign back up after adding my new card. That looks to be an implementation problem though.
What's new is for someone who makes a Twitter client to be able to say "You can buy TweetMaster17000, but it's a subscription that totals $6 a year. That way I can afford to continually update it for existing users."
That's not a bad thing, but it may be a hard sell to many users.
