Several years ago at GameHole Con, Mearls said something along the lines of (paraphrasing from memory here...): There are no plans for a new version. What will eventually happen is a consolidation. You've got class/subclass/spell/etc. info in the PHB, Xanathar's Guide, Tasha's, etc. It's getting spread out. When the time comes, the plan is to gather all of that together into new consolidated PHB and DMG, incorporating errata as well. And, maybe if something gets tweaked for the better (like a Ranger that people actually like), that'll be in the new books, but it won't be a new edition. It'll be a way for new players to have an easier inroads into the game, without making those who own the existing books feel like they need to buy the new books (completionists aside).
So, it makes sense that he doesn't think 5.5e was a good idea.