I'm surprised there's no "CA-tool-as-a-service" where the CA provides an API (and maybe a CLI tool that uses that API) allowing you to automatically request-and-generate certs from their CA server provided it's for a subdomain of a domain you have on your account.
This would be for subdomains with their own "sovereignty"; e.g. Tumblr or Wordpress blogs, where the subdomain "owner" could conceivably want to issue their own subdomains, or, heaven forbid, do client-cert signing for their subdomain.