Smalltalk implementations have had text export/import for ages, and image based source control as you point out, is also quite old, Monticello wasn't the first.
In some way, Smalltalk had/has a more advanced and semantic diffing called ChangeSet
For example, CUIS book, 9.3 The Change Set:
https://cuis-smalltalk.github.io/TheCuisBook/The-Change-Set....
> something else for smalltalk
"ENVY/Manager augments this model by providing configuration management and version control facilities. All code is stored in a central database rather than in files associated with a particular image. Developers are continuously connected to this database; therefore changes are immediately visible to all developers."
https://www.google.com/books/edition/Mastering_ENVY_Develope...
~
1992 Product Review: Object Technology’s ENVY Developer
http://archive.esug.org/HistoricalDocuments/TheSmalltalkRepo...
I think squeak had Monticello for source control with their image based approach almost 20+ years ago and there was something else for smalltalk in the '80s too.
But yeah people like text and hate images, and I believe Pharo switched back to some git integration.