The cleanup and development of Area 51 is an on-going effort, so the list of proposals is far from a fait accompli. Area 51 is in a bit of a transitional state — part feature enhancement and part cleanup work. So let me give you a bit of an overview of where we are on both fronts.
On the development end, we are adding features to Area 51 to enable more communications between proposals. The general idea is to group related proposals into "departments," much like you might group academic disciplines at a university. This will make it easier to add more communication facilities to help these groups of proposals work together and decide how to best allocate the creation of sites between them. More details about how that is going to work as the development efforts continue…
On the cleanup side— As a general rule, I have not been closing duplicates between similar (or even identical) proposals. Nor do I want to rush to judgment about the viability of a proposal. Instead, I generally take a closer look at proposals as they enter Commitment. Once a proposal emerges with significant support, we can make some judgment calls about which proposals need to join forces to create viable sites. Until that time, I don't want to micromanage and stifle people's ideas before they've had a chance to go through the definition and support process. But I do close proposals which are obvious duplicates of Stack Exchange sites which have already been created.
Longer term, duplicates and merging will be much easier for the community to manage when proposals are better organized and we enable better communication. In the meantime, the community is still free to comment within each proposal and you can still vote to close… and certainly feel free to flag proposals for egregious problems.