Collaboration is difficult because of Pro's closed source, commercial nature but I do want to keep as much of the OSS ethos as possible available to customers who want to fix it themselves.
In order to unambiguously own and sell Sidekiq Pro, I must have the copyright associated with the entire codebase. Any work you do which is incorporated into Pro must be owned by me. That's not me trying to be a jerk, that's just the way it works.
If you wish access to the Sidekiq Pro repository so you can send a PR, just open a new Sidekiq issue and include the following info:
You should be granted access to the private repo soon after.