I would love an open-source Heroku. Yeah there's OpenStack, Dokku, etc - but they're nowhere near as easy to use as Heroku (not knocking them, by the way, they have a place and are great projects). Presumably such an application would run on a server of its own and you would give it an API key for DigitalOcean, Linode, etc, and then push your repos to it as you do with Heroku. Massive undertaking, of course.

Something else I'd love to see is a server that's as easy as an iPad. Sandstorm is doing some work in this area, although I'm not convinced that the end result will be great. I want a server I can connect to, install apps from an app store as easily as on an iPad, configure as easily as an iPad, etc. Linux/FreeBSD/etc will always be needed for high performance websites and intensive or innovative computing needs but 95% of people just want to host a website or some email. I should be able to log on, go to the App Store, download the Minecraft server and be playing my game within minutes (with a nice GUI for configuration). Don't believe this is needed? The existence of SaaS is proof that it is - software is too hard and too complicated to install, configure and keep updated on your own server.