I doubt it's even possible for USB3 to support high-end graphics. The bandwith for intensive applications is just not there, and not having direct access to memory (like with PCI-E) could be another obstacle.
Everything is possible, sure, but...
I don't see thunderbolt-like technologies to be an USB replacement, though. More like a definitive standardization of docks for laptops with interesting side effects.
I'm not sure if you're talking about connecting a monitor or connecting a graphics card. Graphics card is easy, USB is only a small multiple slower than thunderbolt, and as long as you have room for the textures 4Gbit/s is fine.
Uncompressed 4k is trickier. It looks like thunderbolt 2 has barely enough bandwidth, and USB 3.1 has barely not enough. No reason to expect they won't have a 3.x that supports it.
Is it still the case that USB causes heavy CPU usage? Even if there was enough bandwidth for 4k video, it'd be a drag if it meant pegging a CPU or two to 100%...
I don't see thunderbolt-like technologies to be an USB replacement, though. More like a definitive standardization of docks for laptops with interesting side effects.