XLRs are everywhere and already installed. You could choose cat5 but it's not as common.
I joked to a friend once that it would be far better if we just used a single connector type for everything in audio and get rid of jacks, XLR, power connectors, MIDI, etc. They liked the idea - I deadpan suggested regular mains plugs and sockets would be good - cheap, ubiquitous and sturdy.
But the advantage of reusing cabling that already exists in 100% of the venues, stages and churches cannot be overstated. It is literally a drop-in upgrade, boom, now a single cable carries 32 channels instead of 1.
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.