I think an actual level crunch only makes sense in a game that either replaces its leveling content, or just doesn't put much value onto it in the first place. WoW can do a level crunch no problem because it redefines what that leveling experience entails, meaning that there's never really a point where you can say 'okay this point pre-crunch is exactly comparable to this point post-crunch'. Meanwhile, say, Warframe... well, wouldn't exactly have reason to do a level crunch anyway, but if it did nobody would really care because nothing is actually moving, you're still fighting the same enemies with the same general tools and very little surrounding story.

I don't think FFXIV would do a level crunch, because to do so would be to implicitly devalue the part of the game you did that to. XIV values all of itself, and that includes the things that happen in the leveling experience, so the devs just wouldn't do something that made Heavensward feel like less compared to what comes after. It also begs comparison with itself by doing so; people are literally going to be able to compare the same points pre-crunch and post-crunch, and frankly, I don't think the post-crunch experience is going to look great, because any given part of the game is going to have us fighting the same things but with less tools. That'd especially do damage to still-popular challenges in the game that are locked to non-cap levels; the deep dungeons, Eureka, Bozja, the Ultimates. Already, a few jobs kinda chafe at those requirements because not every job is designed to be fully capable at level 60 or 70; I hear Black Mage really struggles in the Bahamut and Ultima Ultimates for that reason. A level crunch may well break those things in a way that they can't recover from; beating the Dendainsonne solo at level 60 is already really hard, how do you expect people to handle that at level 30?

To put it cynically: A level crunch is an option that doesn't respect the content that came before it, sacrificing it in favor of what's to come. So it works best in games that already doesn't respect that content.