Now the reasoning isn't present in the patch but it probably is because they want step increments and -fms-extensions is a small-ish first step. Maybe -fplan9-extensions could make sense later, in a few years.
Cool stuff. I've got the same hobby / part-time job (mostly on GrandMA consoles). I have done two-three experiments on custom software to emit DMX which I used for something like four events. For the physical interface I'm relying on MIDI controllers; I first want a software stack I can trust before going into hardware design.
Would love to discuss the topic some more! I don't often meet people with that same interest in lighting that want to build their own tools.
The question is then: is this isolation even useful? There are a lot of attacks that still exist when a program runs in userspace and that are not inherent to GUI programs. Example: creating an executable named sudo somewhere in a directory that is in your ~ and PATH.