I've been doing this exact same thing since march this year with my own domain using MailGun (Free) and custom forwarding rules.
Really amazing to see someone turn it into a product that can easily be set-up by the general folk. (And for a nice price!). Loved your UUID-alias idea.
May I ask however, how do you expect to handle a blacklist of your domains? I've had trouble in the past signing up to some websites that block any sort of custom domains (really bad) in an effort to block throw-away email, what happens if your domain gets blacklisted/categorized as a throwaway email? (Also forwarding to Google and such ends up in "email limbo").