I believe Swen said in an interview recently that they're working on new endings/epilogues and doing content updates, although he didn't mention fixing Karlach's ending specifically. Larian doesn't usually publicize what they're working on until it's ready to go.
They definitely know that the matter isn't settled with the community though, Justice for Karlach is on the list of frequently requested feedback on the Larian discord server and there's still new feedback threads popping up about it. Between that and this rapidly becoming the largest post on the forums right now I think they're pretty well aware that we aren't happy.
