In order to facilitate feature development with multiple developers, the most efficient/effective way to do it is to fork the product repo, then have each individual developer for the fork, work on it, and do pull requests into the first fork. Once the the feature is done, the top-level fork could be PR'ed back into the main project repo.
This is not unlike a feature-branch model, but we prefer not to use that model because 1) it clutters the repo with unnecessary branches and 2) it keeps each repo in sync via fork-synching, whereas a feature-branch can and will fall behind.
So - my ask is that Stash/Bitbucket provide the ability to fork a fork