I believe Cononical's launchpad was built to achieve such workflows. It came out of the need to create an integration platform taking upstream versions of software and applying Ubuntu-specific fixes. In the old days, before git and GitHub won, I liked their bug tracker way over GutHubs as it really supported these flows, where bugs are fixed not in the main repo but by some contributor first.
But we'll, wrong bet on bzr ...
Launchpad is also incredibly opaque to people who don't use it often. It took me a very long time to find the actual release binaries and how to get the sources + build info for them. It was for some nginx modules in a PPA which depend on a newer nginx than what is stock in Ubuntu Trusty. Took literally half a day to get binary-compatible modules built from source (building dynamic modules and they must match all the configure flags of the nginx you're trying to inject them into).
I can see how that that experience would have been poor for you, but I think it's a rather unfair comparison when comparing to GitHub. It's apples to oranges. Launchpad does more than git hosting, merge proposals ("pull requests") and bug tracking; it also manages the build infrastructure of a distribution and the publication of distribution sources and built binary packages. You did get tangled up doing the latter, but the former case is the context of this discussion. GitHub, GitLab and Sourceforge all cannot even do the much more complex tasks for which you had a poor UX on Launchpad.
Indeed. Launchpad has an incredibly bespoke feeling -- it is very much intended for Canonical's particular use case and it's clear they don't intend to spend much time making the on-ramp terribly shallow for new users/admins. That said it certainly represents a massive amount of work and it has a number of compelling features.
