Today, even if small DIY plotters were cheap to build, they’d mostly live in the “art / hobby” space: most users won’t wait several minutes for a page when a laser printer does it in seconds.
That said, it would be great if a simple, well-documented DIY standard (protocol + format) emerged that hobby plotters could implement and that common tools (Inkscape, CAD, etc.) could support out of the box.
I know just about every CAD program, inkscape and many others use the text based DXF. Might be a bit overkill in some cases so perhaps a simple plotting language such as the plot format: https://man.9front.org/6/plot
Hell, some plotters used to come with handbook of HPGL, even
I didn't have a reliable source for pen cartridges though, so I usually saved it for things that were "important" at the time.
Everything else was typed on an IBM Wheelwriter, which in my mind is still the pinnacle of typewriter technology.
Supposedly you can still order the film ribbon cartridges for them online.
Man, I wish I still had it now seeing all the plotter functionality that I was not taking advantage of…