This is interesting for specific use cases. Have you read the nostr state machines I wrote some time ago? It uses dag as you mentioned

gitworkshop - Decentralized Git

Decentralized GitHub alternative over Nostr

Also have you checked cordn by @Besao ? It solves that problem but for mls over nostr which requires strong ordering. In any case you don't need an special relay for this, a cvm acting as ordering oracle gives you that without deployment complexity