> Why would Chrome (the browser) as a windowing system have to be any less efficient than X? There's no reason it couldn't use the same kernel features that X uses. Obviously, just using the framebuffer API would be less efficient, but using DRI and such isn't impossible, and it may be easier to optimize things like video when there is only one video playback widget, which is part of the widget set and provided to javascript, <video>, flash, etc.
If you don't want to use X and you want good performance then you'll have to figure out your own acceleration framework. It won't be a simple framebuffer driver because a simple framebuffer driver provides no means to take advantage of any GPU features.
So, sure, you could possibly do Wayland or recreate the standalone OpenGL application, but for what purpose? Just so you don't have to use XCB?
Wayland has possibilities because GTK is ported to Wayland's native API and Google's Chrome for Linux uses GTK. But even then it's going to require a lot of work on Google's part to reach feature parity with just using what everybody else already uses. Think about multi-monitor support, HDMI output, input hotplugging, etc etc. There is a LOT of things that Xorg does for you that Google would either go without or have to recreate on their own.