Personally, what I think this means is that we need to drill down on how to demonstrate to the players that they have, in fact, "scaled up". Break the treadmill, not by removing the slope, but by making it so players can SEE that they're on a higher point now than they used to be. I don't think 5e's approach is quite right, but it has (again) a kernel of a good idea that can be teased out. Namely: We need monsters that are distinctive to tiers of play. Things that you genuinely "grow out of", and things you genuinely "grow into". Stuff that really, truly is too hard to fight when you're level 3 or 4, unless you've got some miracle--both because that's realistic (there are almost always things too strong for any given combatant!), and because that sets signposts.
Something like 2/3 of 4e's scaling, rather than half, plus progression signposts like this. Clear, identifiable, graspable things that you can say "Look! We did it! We beat <X>!" or "Wow, we just cleared out a room full of <Y> without breaking a sweat, we really have gone far." Non-combat signposts should also get attention, but they're best handled by advising GMs on how to construct them well, rather than trying to artificially create universal ones, which wouldn't fly.