> reusing an existing connector type for a new and completely incompatible role will not make life easier

I don't think it's completely new purpose for XLR, I'm fairly sure I've seen other stuff than audio being pulled through XLR more than once even in professional environments.

DMX over three-pin XLR is extremely common, and it’s also rather common for lighting equipment to be right next to the sound equipment.

Exactly - AES/EBU over XLR has been a thing in the broadcast world for ages. The Behringer WING mixer even has a pair of AES/EBU ports on the back.