I also expect this to be heavily silo'd. That there will not be a way to do this through the API. So we'll still be stuck including the URLs in the tweets, and under pressure from other Twitter users to give it up and use Twitter's client. This will be a battle akin to the argument over retweeting. Many if not most users preferring the old metadata-less way, to the new system-friendly way (I prefer the latter myself). But I think in this case the pressure will be the other way -- to use the Twitter, Inc method of photo-sharing with hidden URLs and fatter tweets.
If Flickr were paying attention, they'd be have a timeline and allow you to follow photo-rivers on other services. And keep it wide open via the API, which works pretty well. Instead their home page is a disorganized mess. By going into pictures, Twitter gives Flickr one last shot at remaining more than an archive of the photography we were doing in the last decade. And not so much a big part of the way we do it in the future.