We’re definitely interested in something like this, but a couple of things are not clear yet.
We’re still discussing what the right platform for this collaboration would be, our current thought is that it should be here, on http://discuss.bitrise.io/ , in the Step Dev category. http://discuss.bitrise.io/ is still quite new, so this is still an “experiment”, but if anyone have any feedback we’re always happy to discuss possible changes/improvements, not just for coding/specs but also for communication.
We think that we still have to improve our docs and our tooling around step dev, hopefully that and Step Dev should make this happen (easy to get started and to write great quality steps).
Definitely! Tooling will help in the future (we plan to add a step dev core plugin to the Bitrise CLI, so that you’ll be able to create a new step with just bitrise step create .., for example), as well as tools like releaseman, but as most of these things are still work-in-progress we’re not happy with the current state. We started to expand the tooling team, so hopefully we can work on these more in the near future.
We also have other ideas for faster step release cycle, like identifying step repositories on bitrise.io when you register one and auto generating a suitable base workflow for them, just like for iOS/Android/Xamarin/Mac/… apps.
Thank you! We definitely have to improve things, and community feedback would help us a lot, so keep the ideas & questions coming! 
We’re also trying to be more open regarding our development processes and about what we work on, e.g. by sharing more and more things in Changelog and here on http://discuss.bitrise.io/ in general.
Our goal is to make it possible for anyone who want to get involved with any part of bitrise to be able to do so quickly and easily, be it a step contribution, guides / How To , or just discussing possible improvements or highlighting pain points which could be solved better (e.g. Support for multiple apk in android workflows ).
As always, any feedback is much appreciated and helps us a lot to see how others use bitrise and how we could make it better.