I don't get how local forks under e4 umbrella provide much added value compared to GitHub. It requires contributors to ask for committer access in order to have this, and the e4 project is kind of an exception to the committer-ship rules set up by the community.
Also, are we sure that at that point of time when people are doing an experiment, they need to be at Eclipse.org and take advantage of the governance? Or is it something that becomes interesting only when contributing back to Platform Core? In later case, then there is no reason for a project to get into e4.
I'm not advocating against e4, I'm more trying to find out more efficient way to bring innovation from non-committers into Platform, and IMHO, that should involve any contributor able to work on a local fork. It's already technically possible, but I believe it would make sense to document it more officially in an "experiment" section Platform's contribution guide where we can explain that either contributor can start a fork (on GitHub or wherever) and then contribute back via Gerrit when ready, or if they want governance from day 1, to consider getting under the e4 umbrella and either work on the sandbox or ask for a fork.