This seems pretty dang useful. I needed something similar for a non-Sandstorm server a few weeks ago and, since all of my domains are hosted on Route53, I wrote this:<p><a href="https://github.com/peterkeen/route53_ddns" rel="nofollow">https://github.com/peterkeen/route53_ddns</a>
Port forwarding would also be a handy feature, albeit a major (impossible?) technical challenge to deal with the varying support for interfaces to set it up. Or perhaps an ngrok-style tunnelling feature (which would obviously be more expensive to run).
Sandstorm is interesting, but I didn't realize it had this sort of DNS requirement. This will also mean it will essentially require a wildcard ssl certificate for people who want to completely host it themselves, which could seriously limit its uptake.