Re: Optional... apparently
>I currently run a Dell mobile precision 5510 lappy connected to their WD15 dock. it uses USB3 protocol on a USB-C physical hole, so only able to drive 1x 30" at 2560x1600 off the DP port,
I seem to recall that to drive a 5K monitor over USB-C, Apple had to go with AMD mobile GPUs. https://9to5mac.com/2016/11/16/macbook-pro-why-amd-gpu/
Something to do with number of video streams and DP 1.2 vs 1.3 or somesuch.