Yep, if 49 is the limit it's most likely gonna be a problem even for uncle jim and them.

Back to running one's own webserver for a sufficient domain server... Or migrating to a few liberal domain providers? 

 Yep. Organizations may move their domains around to different registrars that allow more TXT records too. 

 Yes, but at what point do the performance issues start?

I was reading through this forum discussing around 50 million records on a domain (assuming we get to a point where a successful lightnin wallet provider/implementation gets to at least 50 million users) . 
https://groups.google.com/g/comp.protocols.dns.bind/c/6InK8Qs8R2s 

 i dunno.  @matt do you know? this google article says most domains only allow a max of 49 TXT records. won't Phoenix have a problem once too many addresses are created on their domain?

https://support.google.com/a/answer/2716800 

 If Acinq is using AWS for their implementation they can always ask for an increase on the resource limit. https://i.nostr.build/DHrNj4nC8GrzluTW.jpg 

 There’s absolutely no limit. Some hosting providers add arbitrary limits but even the entire Bitcoin header tree in DNS records running in BIND is like 1G of memory…

https://bitcoinheaders.net/ 

 Any tutorials for beginners? 

 For what? Running bind? 

 Yep. 

 Don’t have a specific one to recommend, but googling “bind authorative server” should turn things up. 

 Thank you. 🙏🏿 

 I have seen no performance issues hosting a few million records on RPis for https://bitcoinheaders.net/

But, BIP 353 does contemplate doing multiple users in a single wildcard record.