Just as a heads up in case this hasn't come up:
Thunderbolt 3/Skylake is 100% capable of driving a 5K display. With the release of the Dell 5K display, Apple added tiled display capability to OS X, allowing the system to treat the monitor as a single 5K image via two spit connections.
2 cables, you say? Nope, 1 is fine.
With Thunderbolt 3, Intel added two DisplayPort 1.2 pathways to the specifications. So built into the 1 USB-C (or optical TB3) cable is enough bandwidth for two independent 4K Displayport 1.2 connections, or enough for 1 tiled 5K Displayport connection. If the USB-C port on a 5K Thunderbolt display was simply that, USB-C, it would not be enough to drive a 5K display. However, given that it's a **Thunderbolt** display, it will probably have Thunderbolt 3 built into the USB-C port, allowing for both Thunderbolt-style daisy chaining and the full pair of DisplayPort 1.2 connections.
In other words, Apple's more than capable of making a 5K Thunderbolt display that can be driven by a single TB3 connection.