>basic technique of "mewing" is very similar if not identical to something that's been practiced in yoga for thousands of years

Can you elaborate more on this? I also assume by "mewing" you mean putting the tip of your tongue on your hard palette right behind your upper incisor, and letting the rest of the tongue suction against the hard (and soft) palette. Surprisingly for something that seems to be so "popular" in "broscience" I find it hard to find any canonical definition or technique.