I think a wiki page and a reference to it in the Git page is a good way to start small.
There we can explain the standard structure that an external modules has to follow for
making it easier to install. I don't know how we can manage some complications like,
for example, the webpack build part for external modules.
I already have some modules, that we use internally in our company (we have a
DisplayManager for setting the display ratio/resolution/orientation), an extension to the
NetworkManager (with capabilities for establishing wi-fi connections) and I'm making
more and more modules as soon as the need comes.
I could help with the wiki page but we have to discuss first how can we make it the
easiest way for the future developers.