Have you ever had to do technical support for someone who changed settings they didn't understand? Or maybe someone who decided to "clean up" a bunch of system files that they thought were wasting space?
In my experience, product design is generally done with a well-meaning attempt to protect the average user from themselves. People who can and do manage their own networks in sophisticated ways are, unfortunately, far less common than people who have no idea that their ISP fscks with DNS lookups.
Personally, I'd bury this setting pretty deep in an advanced-usage-only tab and behind a notice SCREAMING about how using these settings is unsupported. And then tell support staff that they are not obligated to support whatever crazy configurations people cook up for their home networks.
I understand not doing it at all. A few people will complain, but the number of people who will refuse to buy a TV because it doesn't play nice with their pihole is almost certainly too small to register on any material financial statement, and attempting to please them will generally run into some other point they are unwilling to budge on. The number of people who screw up an advanced setting they don't understand will show up in support costs.