For relays thar also accept ipv4 connections, there isn't much reason to do that. It'll only slow things down.
Now, if you want to setup an anonymous, tor only relay, I think it's a great idea
Discussion
I been using tor only relays both on Android and iOS and I barely felt the difference. It doesn’t slow that much
Problem with running one even though I have the hardware is the idea that “those people” are also early adopters of this kind of stuff. Also not a lot of tools to moderate content available I think. I’m all for freedom but last thing I want is disgusting content on my computers. Don’t care about drawings more concerned about real CP or other shit.