As for the ecash mints nostr solution i am not expecting nostr to be used to get the updated mint url like your flow diagram, I'm expecting the wallet to send and receive commands/data over nostr notes, not api calls.  

 I must be missing something…

relays also use dns don’t they? 
how would a mint loose their dns for the mint but not for their relay? 

https://mint.mydomain.com
vs
wss://relay.mydomain.com 

if they use a third party relay… then multiple mint could go offline by attacking that shared relay? 

 I’m not entirely sure. How much does wss rely on DNS? Would assigning a npub to mint and then using wss as the transport medium by a work around using DNS? I need to better understand how these work together.  

 Wss also rely on dns, the nostr advantage is that notes go to many relays, blocking on relay wont do anything, so your wallet and mint won't have one domain as a single point of failure.  

 Oh! didn’t think about this for redundancy. so mints should use multiple relays to advertise their new hostname. 
thanks. cool. 

 whenever a hostname has to be translated into an IP, DNS is involved. 

 If it's done like I said in my comment, it doesn't matter if they attack a relay because the note/commands will go to many different relays.  

 DNS Trusted 3rd parties are security holes.