I was considering creating my own. Creating the UI software is pretty easy using QT (
https://qt-project.org/) or similar APIs.
From a hardware perspective, there are many system on chip that will do 1080p and are really reasonable in price and support an RTOS, if needed.
Effectively, I was thinking of pull together the hardware that would bolt behind a Camaro or other gauge bezel and have the UI presented there. The software would have a canned look but could be customized for some coin.
Boot time is pretty easy to control. The harder part is shock / vibe / thermo / power and potentially latency (esp in an indirect driving scenario), but all of these can be overcome.
With the System on Chip (SoC) solutions available and the capabilities they can provide and meeting the above challenges for just a few bucks more, I'm not sure that a Raspberry Pi would really get you much -- especially if you look into all the other work you'll need to do to get it up and working.
From the MegaSquirt perspective -- I was thinking more in the controlling the dashboard verses EFI and a mobile device controlling it.
Anyhow, basically I talked myself out of doing it because there was already solutions on the market already. I'm surprised about the $20k, though. Seems like it's priced way high for what's provided, IMHO. I've delivered I7 based systems in vehicles for less.