The problem I've got with any signed, cryptographically secure replacement for DNS (including a blockchain-backed solution) is that over time names will be lost. Just like bitcoins get lost.

You need some kind of "admin access" for the system that can fix things like lost keys, at which point you might as well stick with DNS.

or you could stick with losing the names

aaronsw proposed that you could expire unrenewed names after 12 months

i forget what solution namecoin and ens use

I hadn't considered expiry. It lets lost names re-enter the pool, at least, even if not under the control of the original owner.