probably a dedicated domain that you can trust to stay alive and unchanged for as long as possible. so far we seem to not have progressed beyond PURL services, so possibly have a look at w3id.org as they allow defining .htaccess rules which means you can do content negotiation on ld+json requests.
if you feel like a vocabulary you’ve developed is relevant to ap/fedi then you might consider an FEP that proposes adoption/usage of that vocab in fediverse implementations?