There is already a total count of up- and downvotes, but please never add karma to Lemmy. We don’t want to deal with karma farmers and minimal karma requirements to post. I don’t care about the moderation issues because karma brought more harm than good. Please never add that bloody dreadful thing to Lemmy. I already saw a bunch of people supporting adding karma to Lemmy, which will turn Lemmy into a cheap Reddit clone and karma-farming hell. Please, never add karma to Lemmy. I beg you. No more karma hell.
I’m sorry to tell you that an equivalent of Karma existed from the very beginning (though rather than being Upvotes minus Downvotes, it was Boosts minus Downvotes until a few days ago due to a bug). It’s called Reputation and you can see it by viewing someone’s profile in kbin. At the time of writing this, your Reputation points seem to be at 443. Reputation isn’t being used for anything though, and while it can technically be tracked by anyone, lemmy hides that information so far.
[In fact, you can see who gave up- or downvotes to something and you can also see what someone up- or downvoted (or boosted, but that’s a given, since boosting is equivalent to retweeting). This information is out there for anyone to access who spins up their own instance due to how federation works, so the developer of kbin decided to make it public so people are at least aware of this fact.]
kbin is rather new to the scene afaik, so I wouldn’t say reputation has been a part of it since the beginning, but the upvote/downvote records have probably been public since the beginning (idk), so calculating some karma equivalent with whatever preferred metric you wanted was always technically possible, but not socially relevant since average people wouldn’t do such.
Reputation is a kbin specific thing