It seems like this change by Firefox would bypass a pi-hole. Am I understanding it correctly?
Would it be hard to make pi-hole into a DoH provider so you could just point your browser at it? Or does that defeat the "just works" factor of the pi-hole?
In a home LAN configuration, which I'd expect is the vast majority of Pi-hole setups, I don't think you'd really be gaining anything from DoH.
And even if Pi-hole does support being a DoH server, you'd have to configure that in Firefox anyway.