Why do you believe that this will be default on at any time in the near future without a reasonable configuration UI and without a reasonable set of DoH-capable nameservers? Especially given that this would break a substantial number of existing setupts? If you have this little faith into the FF/Mozilla folks, why do you keep using FF? If you’re not using Firefox, what are you concerned about?
The section of people that use it might benefit to a very large degree. Or they can make the switch prominent to push adoption. There are a lot of features implemented and hidden behind “about:config” where you could ask the same question. Many of them are for the security and privacy conscious but come with a few strings attached, for example some advanced cookie settings such as third party isolation.
That said: I fully expect that at some point Mozilla will want to push adoption of this feature, but not in its most extreme form. I’d expect that a default configuration would use soft fallback.
Which I think is the purpose of almost all experimental feature.
In the blog it is clearly stated that they hope DoH implementations will become standard and common, maybe that even some ISP start offering their own.
