[racket] What are the roles for teachpacks these days?

So let's say that I'm designing a new #lang-implemented language.  I'd
love to automatically work with teachpacks and other external modules.
 So I can get require-like functionality with my language, and that
seems to work ok.

But when I click on Language/Add Teachpack, DrRacket responds by
saying that teachpacks only work with the teaching languages.

What's required for a #lang-implemented language to be treated as a
teaching language, and what does it need to implement to get teachpack
support?  Thanks!