There is an older SE Meta question What can be done to keep users active in the commitment phase? at the time it was posted Next Generation of Area 51 was just around the corner.
There is a suggestion to keep allowing the users to refine the site definition. Let them keep voting on questions at the very least, and possibly allow them to create new sample questions. This would give them something to do, which would allow people to keep coming back to the site. by PearsonArtPhoto
Now it is few years later and the "Next Generation of Area 51" is still just around the corner...
I propose implementing the suggestion. In my mind simply removing the lock that prevents updates to the 'phase=definition' tab once the 'phase=commitment' has begun, is all that is needed. I have no idea how the code is written, if this is a simple update or a complex change.
If it is not to hard, it could be a great way to help keep the community involved, because face it, the commitment phase is BORING and it can last several months.