Not too sure if this is a feature or a bug but I've been looking around the changelog and haven't found any answers so far. According to the changelog to Processing 2.0.2:

Experimental Mode has been removed from the default download, so that it can be updated more frequently. Install it and help us test what will become the 3.0 release of Processing! 

However, I've found no ways to install experimental mode, neither through the "add mode" dialogue nor through the downloads page – at least, I don't see any nightly builds there. I'm pretty fond of experimental mode so I'd like to get back up developing with it as soon as possible. Does this mean it'll only be possible to use through building the source?