Thunderbolt 3
A Thunderbolt 3 port will look like a USB-C port. They’re plug compatible. So if you plug in a USB-C device to a Thunderbolt 3 port, it should just work as you’d expect. And older Thunderbolt devices can still be used with Thunderbolt 3 via an adapter.
[…]
There’s also the issue of driving 5K displays. Intel’s announcements about Thunderbolt 3 mention that it supports DisplayPort 1.2, which can drive high-resolution displays, but doesn’t appear to have enough bandwidth to drive a 5K display via a single connection. (It can definitely do it via two cables.) The new DisplayPort 1.3 specification, which is being finalized, is supposed to support 5K displays via a single cable. It would be silly if a brand-new technology like Thunderbolt 3 shipped without the ability to drive 5K displays via a single cable, but that might be the case. We’ll have to wait and see.
Finally, there’s one other catch about Thunderbolt 3 adopting the USB-C connector: Room for confusion. You should be able to plug any USB-C device into a Thunderbolt 3 port without trouble. But if you’ve got a computer (like the new MacBook) that supports USB-C but not Thunderbolt, Thunderbolt peripherals (indicated by the lightning-bolt Thunderbolt logo rather than the USB logo) just won’t work (even though you can plug them in).
Commenters are saying that Thunderbolt 3 does support 5K displays via a single cable. I’ve seen on mentions on Twitter of various other minor caveats, but overall it sounds great to me.
Thunderbolt 3 supports 5K by offering two DisplayPort 1.2 channels over one cable. This arrangement allows a single cable to drive either two 4K displays, or a single 5K display (by combining the two channels, similar to how current stand-alone 5K monitors currently work). A single Thunderbolt 3 cable is essentially virtualizing two traditional DP 1.2 cables.
Monitor support will be determined by what connections the manufacturers offer. If future 5K monitors only support a single DisplayPort 1.3 connection instead of the current two DP 1.2 cable setup, then Thunderbolt 3 would likely not be compatible with those. It might be possible to 'break out' a TB3 cable into two DP 1.2 cables in order to support the current 5K monitors, but I'm not sure of that.
For me, the most exciting part of Thunderbolt 3 is support for passive cables at a 20 Gbps data rate, which would allow for affordable cabling from Monoprice. That said, hopefully the random USB 3 disconnections Michael (and myself) have experienced won't carry over to TB3.