Additionally, I find it interesting to note, that if you had in fact been very familiar with all the work you mention. You should actually have noted that many of these systems go through significant effort to sidestep the GC.
It not just talk about some guys showing up papers at OS geek conferences.
The Oberon Native for example, was for long time the main operating system at the operating system research department at ETHZ. Most researchers used it as their daily OS for all tasks you can think of.
The GC was done at kernel level. Besides Oberon code, there is just a little bit of assembly for the device drivers and boot loader.