One thing that keeps me away from EMF is that I'm so used to hibernate persistence and good old java beans. You may rant on that. But I have a look at Teneo and CDO from time to time, things keep getting better.
But think of if we had something like CDO running on Datanucleus ? It will give us the power we need for EMF in the cloud. Theres support for googles app engine and the new VMForce PAAS will be running Datanucleus to. I would defintively be thinking about using VMForce if I had a EMF persistence solution like CDO running inside.
If I only had more time... Maybe theres something like this out there and I just haven't heard of it ?