Re: [Git/Wiki] please review the proposed workflow and comment

[RIAstar]

which branch(es) will non-committers have to target?

I would say, its own branch, I mean a branch with the name of the 
relative issues in the JIRA 
I don't think it is possible to directly target a new branch. The target 
branch must be an existing one.
I don't know if the committer handling the request can decide to pick 
another target branch than the one that was chosen by the non-committer. 
(Haven't handled many pull requests myself and definitly not in complex 
projects like this.)