Wow! what an interesting idea, but how the decentralization mechanism is going to be regarding hosting those codes?
Regarding merge request approvals, I think the approval mechanism could be as same as the proposals one. Once a merge request reaches 100%, that merge request is merged.
The code would be on e.g. Github, like I mentioned to Kyle. A pull request creates a Hive post. Maybe the contributor can talk about his pull request in the Hive post. If it's merged, then all supporters of the project give that post a vote.