I am in the process of building a new mini-pc for my RST-135. I just noticed that Framework is offering their mainboards for purchase now; they are comparable to 11th generation NUCs. They also have all of the CAD files in a GitHub repo; several users have designed cases and other accessories.
While not everyone's (or most) cup of tea, for anyone who wants a semi-custom setup at a fair price, I figured I'd point it out. I am going to try making a custom Eagle-like PC out of this for my portable mount.