Sadly, I was unable to find references to what I saw, but it's pretty trivial to think of such a system, although, again, domain names won't be mnemonic.
For mnemonic names, there are already many solutions which have been developed, such as .BIT and .ETH domain, as well as others with different goals. There is also GNS, although I'm yet to study it: https://www.gnunet.org/en/gns.html 

 Oh, ok, @mbarulli, here it is: https://dnstr.org/