Not a pi-hole user, but what is the plan for pi-hole once encrypted dns is everywhere? Will it just be dead? I can’t really think of a way for it not to be.
DoT isn't a big problem for a pihole, but it doesn't look like things are going that way. DoH can only be blocked by a mitm proxy. You would have to take a pretty serious security hit to do something like that with a pihole.
Whitelisting would make it much more difficult for wildcat DoH. On the gripping hand, whitelisting is extremely annoying and tends to block more work-related-and-useful than software that is actually malicious.