All you’d need is the ability for a client to add ability to filter to specific views or modes to only use certain relays. For example, create a Twitter mode which only shows and posts notes to 140 char relays (you tell the client which relays are 140 char relays)

I think nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s is working on this already with Damus and filters. Not 100% for sure tho.