DNS challenge is complicated by the fact that every registrar has their own API. HTTP is easier for nginx because it’s a single flow and it already does HTTP.

I’m sure nginx will get DNS but it’s still an open question when it will support your particular registrar or if at all.

> DNS challenge is complicated by the fact that every registrar has their own API

You can sidestep that by delegating the ACME keys to your own name server.