Filed upstream: https://secure.phabricator.com/T6008
A web based code contribution process would lower the barrier for new/casual contributors, as well as technically simple improvements such as source code documentation, HTML/CSS files, and so on. GitHub has this feature and it makes a difference.
This use case is real for #Wikimedia, where we have a big community of gadgets, templates, bots, and docs writers used to a wiki interface but not so much (or not at all) to a Git based workflow and its tools. This could be a potential are of focus for us after we are done with our current Maniphest-centric migration.