The only way I’d be okay with a X/XI/XII and beyond is if Kylo has offspring that the next trilogy focuses on. Numbered saga films should be about the Skywalkers at this point, otherwise they should be a separate series that isn’t Episode X/XI/XII.
Of course, if Lucas hadn’t made I-VI into “The Saga of Anakin Skywalker,” I’d be fine with IX being the last we see of the Skywalker bloodline, with X-XII having nothing to do with that family. But since that’s what the movies turned into, there’s no reason not to begin a new saga that isn’t Episode X+ if they aren’t continuing the Skywalker family past Kylo.
Lucas making it into “the Saga of Anakin Skywalker” or “the Tragedy of Darth Vader” became irrelevant the second they announced Episode VII, just as the OT being “the Adventures of Luke Skywalker” became irrelevant as soon as the prequels were decided. Now they’re “the Skywalker Saga,” which means that yeah, they shouldn’t make any more if all the Skywalkers end up dead… but then again who’s to say they couldn’t reframe the saga again like they’ve done before…