It's a big problem for accessibility. Modern web pages are a nightmare for screen readers, for example. Tags which explicitly mark where the navigation is, am

It's a big problem for accessibility. Modern web pages are a nightmare for screen readers, for example. Tags which explicitly mark where the navigation is, amongst other things, would be a great help. I'm not sure that I see the value of just being able to define whatever tags you want, though. Sounds like a recipe for disaster to me.