The "Texture Healing" feature is a really smart use of OpenType features to make problematic monospace combinations look much better without breaking the grid at all. One naive way to do this would be to create ligature pairs for difficult pairs (mi, lm, etc). But instead, they seem to be selecting character alternates that fill the fixed width differently based on their surroundings.
Commit Mono font does something similar and calls it “Smart kerning”. Visit https://commitmono.com/ and click on the “04 Intelligent” tab for details. In practice this is unusable. Because the width of the letters now depends on the succeeding character, the text jumps as you write it. Super annoying. Cool for reading. Awful for writing.
If the editor “repaints” commit mono on the letter-pair boundary, I could see that being a very jumpy UX — ie: the letter I just typed is moving by a few pixels. But if that repaint happens on the word boundary it might be less noticeable?
In either case, a transition could be helpful for commit mono and/or Monaspace. (But agreed with above comments that Monaspace is more subtle because it spreads the spacing over the entire word, so maybe the transition is not actually percievable or worth it). :)