this is also something that is a bare minimum for forums & social media sites in 2017...
the ability to like and/or thank a user for their post in a nice feature to have.
And list with users that gave 'like'
'Likes' are very 2010, I think we should have a system like 'stars' or 'hearts'.
I'm not sure about listing the users who gave the like as that makes optimising the thing trickier.
If it's just likes on their own, you can just slap a new column on the posts table, otherwise an extra join might be needed.
There could be an option to show users who have liked (limited to the last X, like I do in my SimpleLikes plugin). Having a simple like counter isn't quite as informative or useful IMO.
I think this would be a great feature but on really big boards like the one labrocca owns, this most likely would be a feature that would need to be disabled as he has mentioned in past times.