XPS 13 (9350) succesfully connected to HDMI 4K@50Hz and 4K@60Hz!
Thanks for the update today Dell!
Been using my XPS 13 (9350) on 40" 4K monitor on TB15 dock and HDMI for a while at 30 Hz. Today, installed the updated video driver (2016-09-07) and got 50 Hz and 60 Hz working with Plugable adapter! So, no need for the TB15 until it can also support 50 Hz or better