> nextdns.io does a really good job of running such a service.

It is not trivial to build, run, and operate a nextdns-esque service. The founders, Olivier and Romain, are some of the world's best at what they do, imo.

That said, a client-side DNS re-write solution might be relatively cheaper to implement and might even be a tad-easier than deploying an global DNS resolver with per-user custom configurations and endpoints.

Agreed; it's definitely not trivial. We will definitely tackle mobile very soon, and this is a potential solution. Thanks!

Thanks for the suggestion - yes that is definitely something we've thought about and will possibly implement. We'll be tackling the mobile problem soon, and we hope to use our learnings from desktop to find the most effective solution in mobile.