Yes, a Drupal site could act like a relay. I have thought about that.
As I understand it correct, your idea would be using the Drupal backend (PHP) as a relay proxy for relaying events kind 30023? 

 Yes or eventually any type of content, basically leveraging Drupal as a CMS for nostr content, could be products, articles, etc 

 For me Drupal is like a swiss army knife for content management in the same way Nostr is a swiss army knife for content / data publishing (broadcasting)