This is actually pretty similar to what we've got so far internally at ep.io, albeit without the procfile and with a slightly more complex definition instead.

We're even running things like Redis instances off of a similar codebase, albeit one modified so the >1 server case is different.

Edit: Oh, and of course we're not exactly as open and launched as Heroku are. Just pleased to see that other people think it's a sensible way to build this stuff!