It would be nice, but I'm really strict about adding "plugins". The way the forum software works, plugins actually "modify" the code. That makes keeping things up to date (especially of concern being security updates) much more difficult, because the standard patches do not apply cleanly. Instead, I end up having to manually apply the code changes (a lot of work).
While not quite the same... what IS in place is a connection with the Facebook "like" button. At the upper left of most pages, you can like the page. It's not quite like liking the topic. It actually likes the specific URL, which for multi-page topic ends up being whatever page you're viewing. And that's not the same as liking a single post, unfortunately.
So... sorry... but that's not likely a feature that will get added. I do like the idea (no pun intended)... but I don't like the idea of the significant addition work it creates on an ongoing basis.