In my epilogue I had Lae’zel and her mission to talk to with the big important Githzerai guy whose name I cannot remember or pronounce, Gale inviting you to his magic school to talk with his students, Karlach and Wyll going to fix her engine and me trying my best to resist the urge to devour the brains of my fellow companions as a mind flayer (that one was a big surprise when it happened!). With how many possible permutations to the ending there are, I think the most realistic one for a DLC is the straightforward Karlach + Wyll (and possibly you) going to fix her engine, at least that one only has like 4 possible outcomes from what I recall (who goes with Karlach, and if Tav is a mind flayer or not).