Isn't there room in the Drupal core project to expand Drupal so that it either includes social networking features like image and movie uploading and galleries, chat, IM, and others, or so that the administration UI provides for a social networking-centric menu/layout? Perhaps you could have a whole social networking management section, or a whole media management section? Maybe Drupal could use an API to more easily allow for media and social networking modules to be easily added and would help integrate features like tagging across all other Drupal modules. Just having this last feature to make social networking and media modules more integrated with one another I think would help tremendously and would cut down on developer time integrating manually.
I think the first suggestion, expanding the core feature list of Drupal by including this capability, would be best. If one was worried about download file size, at least make individual modules easily installable, preferably through the UI like Joomla. The important thing is these must be considered part of the main Drupal project so the modules will look consistent and polished.
For videos, with HTML5 you wouldn't even need complicated players, just ffmpeg for your video conversion backend.
I found these two links but they haven't been updated in 1-2 years: