I love how many interviews Larry Tesler did (he passed away in 2020), he was so influential and it's interesting to see what that looks like from the inside.

Gypsy (that first modeless editor) recently turned 50 years old and I wrote about it here largely from those first-hand accounts: https://digitalseams.com/blog/the-gypsy-document-editor-cele...

And it's not mentioned in this ACM interview but rather this one with the Computer History Museum https://archive.computerhistory.org/resources/access/text/20... that implementing a modeless editor was easier too, since you could use a simple case-switch instead of having a bunch of explicit modules for each mode.