Colin D. Devroe (who recently left Viddler to work on a new not-yet announced project) has written quite a bit on the future of Flickr.
I think his suggestion for having a mid-size account is a pretty decent idea, but it has to be done carefully to avoid cannibalization of current accounts. I feel as if most people currently paying for Flickr Pro don’t take advantage of all the features offered. I might even go in the other direction and have the current Flickr Pro offering become the mid-size account, and offer a more expensive Business account that doesn’t have file size or video limitations.
Whatever their strategy for success may be, Flickr must evade further stagnation in order to be competitive. They can’t ignore and leave new markets wide open like they did with mobile. They have the opportunity to become a powerful weapon in the hands of Yahoo. Right now it is just an untapped resource but it could be forged into something that makes Yahoo again seen as a formidable opponent.