Hmm...
(Leo, edit your "could" in the OP.)
I see Steve's point. It's meaningful.
In the past, entries could get liked/shared off for other sites - like Facebook, apart from blogs shared in the user's own one.
We do not have blogs now; however, it could be interesting if we'd obtain a possibility to like/share topics on(to) certain other sources - like WordPress, Facebook, like that...
As to the suggested liking topics right here, I'd speculate on that if the engine could count how many people have starred the discussion and, when a certain number's reached, rate the topic in a way... Like a badge for the topic<_<