Unfortunately, with DoH, this now means that I have to go scorched earth and block all common DNS server IPs at the firewall. You use my gateway to resolve (DNS - 53) or you're out of luck.
I suppose it's only a matter of time before even the cheapest IoT junk just establishes a VPN to its maker's cloud and sends zero unencrypted traffic.
In your specific case, that means that while devices should offer a configuration setting for which DNS server to use, it shouldn't be via blindly listening to the possibly malicious DHCP server.
Because you shouldn't be able to control other people's devices just because they happened to connect to your Wi-Fi. And you don't have to configure them all individually anyway: you can use Group Policy, MDM, etc. to configure that setting on your whole fleet at once.
Why? If it's my network, why should I not have control over all the traffic on it?
This is me, with the caveat being that it's my damn device. It's only the OEM trying to say it's theirs and that I'm "censoring other people's traffic". If I bought it, I should be able to do as I like. If I tell it the DNS server is local and/or that domain is elsewhere/non-existant, I don't want it deciding otherwise and sneaking traffic out over port 443.