Here's my perspective, as someone who played WoW back in 2004-2009 and hasn't done a lick of research into the mechanics of how Blizzard is actually going to implement the game, but who nevertheless is enthusiastic about joining the Classic Wow Bandwagon:
This is a non-issue. The only reason I even know about layering is because of sad sacks moaning about it in this sub on a daily basis. Could it inadvertently remove a lot of player interaction and produce some dead zones where there should be a higher density of players? Possibly; according to you all. Could it improve server performance and reduce stress on the server side and provide a smoother overall experience in terms of performance and stability? Possibly; according to you all.
But here's the real hypothetical - and also rhetorical - question: Is anyone who doesn't incessantly obsess over this nerd rage-exclusive issue going to understand/realize/care about it? Not unless it's basically the worst case scenario spelled out by the doomsayers on this sub. The most likely outcome is the vast majority of people won't notice they're being layered for every 9/10 times it happens. Layering is probably going to be fine, and if it isn't it'll get tweaked.
Can we all get back to talking about which class builds we want to main as, now?