That sort of decoupling could be fascinating. IMO, the walls may be as much a function of economics as physics.
Running a small number of powerful radios on low-frequency spectrum is a cost-effective way to cover large areas. Physics constrains how much of that can happen in the same area. But if networks are willing spend cash, they can get a ton of capacity by densely deploying high-frequency radios. Don't think we're anywhere near hitting the walls on what's possible there.
Putting this another way, networks provide enough bandwidth for everyone in Manhattan. It's just expensive.
It won't help much. Radio waves start getting too much attenuation to be useful outside the LoS around 5GHz.
That's still not a lot of spectrum. And you need to share it with other consumers (WiFi).
Then you start getting into the practicalities. You'll need to spam EVERYTHING with your access points. Can you imagine dozens of different wireless providers installing access points on every floor of every building? It's just not going to happen.
Running a small number of powerful radios on low-frequency spectrum is a cost-effective way to cover large areas. Physics constrains how much of that can happen in the same area. But if networks are willing spend cash, they can get a ton of capacity by densely deploying high-frequency radios. Don't think we're anywhere near hitting the walls on what's possible there.
Putting this another way, networks provide enough bandwidth for everyone in Manhattan. It's just expensive.