Maybe I'm really dense, but this is just instructions for agents on how to write code, whatever that code looks like.
What is the difference between asking an agent to write these new two DSL's and asking an agent to create or customize a django template, or whatever?
I know the job market is tough, but devs are not working on the user side of WYSIWYG email editors. They were creating templates before, and they are doing it now, why would they use this?
These DSLs are not there to replace templates. They are to define email lifecycle: those are different things. Email lifecycle dictates "who" gets an email (ie anyone with a Pro plan) and "when" they get an email (after they upgrade to the Pro plan). Template defines "what" they get (the email content etc). Those are different things.
You can do the "what" part (template) via WYSIWYG or django template or ReactEmail,... Sendlang is the equivalent of your django code but for the lifecycle part.