UPDATE 11
After some minor tweaking and additions, the GitLab dev repository for Escargot’s Yahoo! frontend has finally been updated! 
If you want, you can also checkout, or download, the files from the ‘feature/ymsg’ branch and test everything for yourself, as long as you have Python 3.6+ and a command-line set up for the occasion. (More detailed instructions on how to do this here) 
And here’s the appropriate version of Yahoo! Messenger to test this with: Download Yahoo Messenger 5.5.0.1244 for Windows - OldVersion.com (This build is more stable with modern operating systems than build 1237 of Yahoo! Messenger 5.5)
More news will come whenever.