GeoJS is available on https://get.geojs.io/. The HTTP version redirects to the HTTPS version, as such a non-HTTPS version is not available. There is no plan to ever change this.
IPv6 and IPv4 only endpoints are available on https://ipv6.geojs.io/ and https://ipv4.geojs.io/ respectively.
Just hitting https://get.geojs.io/ returns some plain text information about your IP, try it out!
As it currently stands GeoJS has no rate limits and doesn't require any to be implemented. Should rate limits be required advanced warning will be given where possible.
Our endpoint documentation is over here.