Once that is said, it should be possible to work in a general-purpose open source 2d printer. The open community has achieved bigger goals. The biggest problem I can see is the entry barrier: to get a very basic printer, you have to invest thousands of time with a lot of knowledge in different areas, when a basic printer, even from the large companies, is not very expensive.
I think that one of the only chances we have for that to happen is that a company frees its designs and patents and community starts working from there.
It'd probably be easier to make a nice block alphabet for a plotter and then just print your documents as biro drawings.
But again, feeding paper seems like a very fiddly problem.
OTOH hacking an IBM Executive might have been something. Proportional spacing!! (but a much fiddlier mechanism)
I had for a while a NEC Spinwriter--loud, slow, built like the proverbial tank. My recollection--it's been more than 30 years since I used it--was that it did support proportional spacing.