Its definitely come up! I think it would be cool to have a community working on the translations to MJML from Lexical. There are so many corner cases and email clients out there, it's definitely a challenge to get things working everywhere. What type of compliancy problems have you run into?
I would really like to eventually open source core parts of Loops.
I think parts of the editor makes sense, including the MJML. We spent an entire weekend extending MJML for Superhuman and it would be cool to release that work some way.
Runs kinda counter to your business-case I suppose, but might help someone (me) out :)