I toyed with the idea for a bit. The first question was what would a app add over a the mobile site and setting the bookmark as a icon on your homescreen.
Mobile site is good enough. I could add notifications for @mentions and private messages. That is about all I could think of.
It would be a considerable amount of work for a niche thing when I could make more doing real work.
But if wan’t to give it a go to get your feet wet and build a portfolio give it a whirl.