Honestly I have not looked into it so far and hope you're right. We also use a number of addons, though I don't think any would be too difficult to replicate.
Regardless, it's a significant amount of work for a startup with just a few engineers, perhaps a week of two of distraction. I expect a bunch of "how to migrate off of heroku" blog posts will be out there shortly.
Thanks very much for the blog post idea, I think I'll do something with that!
FYI you can keep all your Heroku addons inside your Heroku account while utilizing them from a server outside Heroku. For example, if you use the "Redis To Go" Heroku addon, you can fire up your own EC2 instance (possibly through AWS Elastic Beanstalk) and connect to your Redis To Go instance using the same connection info. The main difference will be that you won't have access to Heroku's environment variables that you're using now, but you can use a config file instead.
Regardless, it's a significant amount of work for a startup with just a few engineers, perhaps a week of two of distraction. I expect a bunch of "how to migrate off of heroku" blog posts will be out there shortly.