Would be interesting to see a design system that somehow sits in-between these two extremes. I've got no idea what that looks like.
I may have already gone too far with the proportional text.
It's a bit depressing to watch the HTML/CSS users go through huge contortions to set up a reliable cross-browser typographic grid (i.e. a consistent line-height) and equally-spaced 12 column layout. On the VT100 you get all of that for free. :)
I don't think I've ever seen anyone explore the concept of mixing proportional fonts with the standard 80-column monospaced character-cell display. One problem to solve is how to inform the program driving the terminal about the font metrics (i.e. width of each character) -- this already rears its head when showing UTF-8 text on a terminal thanks to CJK full-width characters, but in that case the width is always exactly 1.0 (half-width) or 2.0 (full-width) and isn't a property of the terminal's current font.