. . .And at long last, KiCAD 7 brings the TTF/System Font support I was hoping for!
I was waiting for that as well, but note that currently KiCad's handling of TTF fonts is very slow and makes opening schematics (including switching sheets, which makes it more obvious) much slower.
This is a known issue that I can't tell whether the maintainers will be able to address any time soon.
Also, the graphic rendering is not super great (at least compared to native rendering of fonts) as it's rendered by OpenGL and probably characters are transformed into purely graphical objects (as for the standard KiCad font), which would explain both the relative slowness and the "meh" rendering. Fonts are hard to render. I was hoping that text would be optionally rendered natively, but I guess it wouldn't fit at all the view model of KiCad's schematics (and PCBs.)
So, while the feature is great, the result for now may not be as good as you'd expect, at least from a UI POV. But for printing/exporting schematics for publishing purposes, and for custom fonts on PCBs, it's great to have.