They local/private cloud and the official cloud will not be exactly identical, but from a feature standpoint they will be close:
Here is what the local cloud will not have:
Scaling
Distributed data storage
Auto failover
Distributed compiling
In addition the RootCloud server and the web IDE are two separate servers right now, and the IDE depends on lots of services - we'll either release a desktop IDE (like Spark did with their Atom based IDE) or more likely we'll rework our web based IDE to be part of the RootCloud server so it can be used locally and/or standalone.
The goal is to have every platform feature available in an open source package - but that package will be designed for single server standalone use, you can connect a ton of devices to it but you won't be able to point-click-and-launch a 5 million device cloud.
We have no interest in steering anyone to our official cloud, in fact if you don't use it, we save money in resources! Our only interest is making sure it isn't super easy for a company to grab our server and launch their own auto-scaling knockoff - which is a very real concern for us because, for instance, the "Digispark" branded clones from china sell about 10x as many as the official Digisparks - and so many of them don't work that over half of the support emails I answer are from people who bought these fake devices and can't get them to work.