"to discuss and hash out possible proposal mergers"…
The discuss part of that equation is what is generally lacking in Area 51. There is currently no effective intra-proposal communication between participants.
We have implemented the means of merging proposals — features that even allow users to vote on that merging. But, without that communication component, we've been really hesitant in deploying those features. Users would be voting blindly.
To date, merging proposals has been a somewhat manual process. It generally consists of looking at proposals which have entered the Commit phase and considering whether the proposals are better served by merging with related proposals or integrating the subject into one of the sites that has already been created. Then I'll contact the participants to suggest supporting a leading proposal or to discuss whether related proposals should be merged at all. There has been no physical merging of proposals. "Merging" proposals has been accomplished mostly through consensus to support the leading proposal.
Discussions amongst the music proposals have not reached a consensus. To get them merged in a way that makes any sense, it is going to take either an executive decision or building the tools to allow the extended discussions that are needed.
Efforts are currently going into both ends of the equation: Working our way through the proposals that need a bit of manual intervention… and building the tools that will allow the community to handle these issues on their own.