Well, the alignment is a pretty significant downside. There are now some excellent mono faces that have broken from a lot of the traditional monospace design e

Well, the alignment is a pretty significant downside. There are now some excellent mono faces that have broken from a lot of the traditional monospace design elements and that look and feel very much like proportional fonts. Quadraat sans mono, cartograph cf, triplicate, I've seen a good homebrew alegreya sans mono variant too. I don't know of any free ones, though inconsolata-g is well in that direction. But I expect more of this trend over the next few years.