a) It needs dns resolution that is not available on webapps unless using a proxy server or DoH provider, increasing centralization
b) Very limited control over cache invalidation by the domain owner
c) Relies on the user or the user's os to set encrypted dns for privacy
is critical for censorship resistance. We already see LNURL-pay recipients filter who can send based on source IP address, and its absolutely a legal requirement for companies to do so.
No it doesn't, the application making the query can choose how they make requests for themselves.
While public recursive DNS resolvers are very common (e.g. 22.214.171.124, 126.96.36.199, and 188.8.131.52), using such resolvers directly (even after validating DNSSEC signatures) introduces drawback (b), at least in regard to a centralized intermediary. Resolving payment instructions recursively locally would instead introduce drawback (b) directly to the recipient, which may well be worse. For payers not using VPN or other proxying technologies, they generally trust their ISP for protection against denial of service anyway, so using ISP-provided recursive DNS resolvers is sufficient.
Huh? You can pick a TTL and requesters will cache for exactly as long as you say. This simply isn't true.
With your system you reveal your ip and payment intentions to the dns resolver that is a centralized entity that can absolutely filter out records, requests and log your ip. That is even more true if you force the dns resolver from the app to use DoH as suggested. You even said that yourself, in the BIP and you suggested to use isp provided dns...
As i've said...
TTL is not guaranteed to be respected, DNS is not intented to be realtime.
TTL it is just an expiration, with http headers you can control much more than that.
There is a moving goalpost here
sometimes it is about privacy : but you've admitted in your BIP that there are drawbacks
sometimes it is for size or complexity of the sw stack
sometimes it is for censorship resistance: but if that's the goal we should probably avoid dns entirely, since there is history that proves that dns is very easy to use for censorship, see for example thepiratebay that is dns blocked by many resolvers. Why do you think they would never block or track a very specific dns query? You just need one law that mandates that, actually, very easy.