I've been really excited for this for about a year now, and have been having a great time playing with the pure Git workflow. If you look at this problem in one direction (only does Ruby, won't kill the AppEngine), you're probably missing the point.

We were about to bring our apps to Engine Yard's Solo EC2 management system, and Heroku's essentially deprecated similar offerings from a bunch of companies all over the place.

I'm sure adding new technologies and languages will bring more people over in the future, but for now it seems like this platform could end up being a great reflection of the current state of the Ruby, with our preference for all things distributed and collaborative like cloud hosting and Git source control.