We have plans to eventually have a more feature-rich editor on the front end, where you can edit tags and delete the post. Categories from the front-end aren't in the plan, though, nor is editing images. Image editing is too complex at this time to be done from the quick-post area on the front end.
But, don't give up yet—I've seen a lot of activity around this on the WordPress.org forums, you can take a look by search on the P2 "tag": http://wordpress.org/tags/p2. There are companies and individuals who've modified P2 to add category pickers and other features, so you might be able to ask them how they managed it.
Hope that helps, and thanks for your post.