I still work on it for people who ask. I'm working with a team on a rather large c2 project right now for a tv network. I'm bound by my contract so I can't discuss it, but yes I do still work on Facebook and other integrations. I just changed from a pay once for a plugin to an I'll work on your project with your team for a fee.
Facebook isn't overly difficult to add. It's just annoying to keep updated for use in newer projects. But to answer your question. I'm usually tasked with adding feed sharing(stories) or picture, uploading to a users page, or Facebook payments.
Less often I'm asked for adding scores, achievements, and gifting.
The above is typically all anyone ever asks for. The only truly difficult task is adding the Facebook payments.