The fundamental issue is that Clients recreated Web 2.0 with a user-defined CDN by making Relays a Profile-level, rather than a Post-level setting.

Relay Groups selectable at the Post level in all Clients is required for this use case to ever work.

Otherwise, Clients literally break the attempt to have a topical or anti-topical Relay. Because everyone using a Twitteresque Client with your Relay in their Profile settings will blast all their off-topic thoughts to your Relay, too.