Ian,
We're actually in the process of bringing up a new developer just for 3rd party integration of things like Zoo. It's definitely taken too long, but we're hoping/planning to get some Zoo-specific features in next month (July). Obviously, I've said it's coming soon before though, so I don't want you to base all your plans around it.
The 5.1 release will also have some more generic sharing options that can be used with any extension, and shouldn't require as much custom-code (like a plugin). The plugins for Open Graph will always make things easier, but our goal is to make it so anything can be done without them.
Now, onto the most import question though, can you let me know *what* integration you're looking for? There's a lot we do: automatic like/comment boxes, open graph tags, open graph actions, and profile import. Everything won't be there from day one, so if you let me know what you're looking to do, I can tell you where it falls in our priority list. Our user's feedback is also what makes our priority list, so that will help us gauge things even better.
Thanks,
Alex