I'd stick to monospace fonts for text editors

This supports being monospaced by the looks of it - scroll down to the tabular data feature. The font really has a wide variety of options.

It's tabular numbers only, not letters.

And "automatically monospacing" any font that is designed proportionally will look terrible, so stick to an entirely monospace font.

Even if it's a SaaS app for general writing, not a code editor? (I guess I should've clarified this right away)