I will be following this with some interest, honestly I probably need to subscribe to it as much if not more than contribute to it. In many ways just the template for documenting conventions may be most useful since my farmOS may be less conventional than some with customizations (for better or worse I just can’t leave things alone 
).
Perhaps the same conventions document should be supplied when appropriate with custom modules.
Could that field reference some sort of entity that stores the convention and/or a link to its repository?
That in its self could do with a convention! Lots of possibilities from referencing enterprise type (fruit/veg/beef/dairy/poultry etc) to region (EU/US/IRL etc) or a specific QA scheme.