This seems to have significant overlap with
https://www.mediawiki.org/wiki/Requests_for_comment/Improving_extension_man…
.
Personally I think we should standardize around one tool and Composer seems
the best positioned for that. So instead of maintaining N competing
solutions with different strengths and weaknesses and leave the user to
ponder which one to use, I think it would make more sense to focus on the
holes in the Composer workflow and write small tools to plug them (e.g. a
web interface to use Composer on servers without a shell access, or a way
to disable/re-enable extensions without fully uninstalling them).
In that spirit, maybe writing a composer.json (or composer.lock) generator
could be a good way of making the extension + git branch selection user
friendly? Once you know which version of which extension to install,
Composer should be able to do the job. The generator could even be a web
service with a nice GUI, like the short url builder (which rocks by the
way, thanks for maintaining it!)