Have you considered adding a second HDMI display via a small interface board?
ThinLinX is planning on adding TLXOS support for the Rock Pi 4, we specialise in Thin Client and Digital Signage Software.
A second display would be very attractive to customers looking for a low cost, high performance Thin Client or Digital Signage device
We would design our own plastic box that supported the second display and designed to also fit the large Heatsink that you have recently released
Thanks
John
Hi
Second HDMI display would be cool.
We have only exported two lanes MIPI over the DSI, same as Raspberry Pi. I highly doubt it can works with 1080p@60. Have you got the second HDMI working on Raspberry Pi?
Cant he use the usb-c as display port and power it with GPIOs?
For the Raspberry there are MIPI-DSI to HDMI adapters. Not all work well.
Hi Jack & NicoD,
Thanks for the quick responses 
We developed a second display solution for the RPi which uses a RPi Zero which is booted, networked and powered over the OTG Port.
For this to be useful we had use a Citrix binary and a single Citrix Library to allow us to have dual screen Windows 10 Desktop which was a VDI machine running on a Server. The connection was Citrix HDX and delivered very good performance.
We have have tried USB Displaylink adapters but the performance was terrible…
We have not tried MIPI-DSI to HDMI yet as most of them seem expensive
I like the USB-C to HDMI suggestion, the cheapest one I could find online was about $20 which is pretty good, the only other cost would be a USB-C Male to Dual USB-C Female connector, I found one of these for $3. Using one of these you can plug in the Power and Video adaptor at the same time
If this works well it is a very good option for anyone wanting to add a second display
The usb c on ROCK Pi 4 is only for power and data communication with power adapter(QC and USB PD protocol). There is no display in the USB C.
Thanks for the Reply Jack, looks like the only option is to use a MIPI-DSI to HDMI adapters