For a while I was doing my own PESOS for my tweets so that I could still reply to people from the Twitter app and get those back on my site as posts. I quickly ran into a problem where I was sometimes re-importing a tweet that I had originally POSSE'd and would end up with two identical posts on my site. I wouldn't even know where to begin to try to do that with Facebook. If bridgy solves this well, I would probably use it, because I gave up running that code myself because of all the edge cases I encountered.
I am planning on doing PESOS of my Instagram, Twitter and Flickr likes, since I still often find myself in a situation where I'm reading something on one of those silos and it's quicker to just tap their button. I would happily use a Bridgy version of that as well.
You shouldn't be afraid of writing a micropub client for this, since it's basically a version of OAuth 2.0 which you've already dealt with on Instagram and Facebook. Also most people so far have implemented non-expiring access tokens on their sites. If you wanted to make this explicit, you could add a scope to the authorization request that would indicate such.