TL;DR Subtopics of sites in beta are themselves heading towards beta. Is the sub-site method not a more appropriate implementation? Comments both on Area 51 and B&CG that seem to indicate that the people who are interested in these topics believe this would be a good solution instead of separate sites. The responders in this Game of Go thread have specific concerns that would need to be addressed.
I will open this discussion with an acknowledgement that the mini-site idea that was implemented for Facebook has been specifically noted as unlikely to appear on other SE 2.0 sites.
With that out of the way I would like to suggest that it could be exactly the solution that could help Board & Card Games. This question on Area 51, and this answer highlight part of the issue - there are many proposals to start game specific SE 2.0 sites alongside B&CG; Go and Magic the Gathering gaining a lot of steam.
I can see their point, to some degree, that users looking for specific information on a particular game will look for a specialized site as opposed to a general one. I believe gaming.SE also fights this particular problem.
There are a couple of specific proposals that could likely bring in a reasonable number of users to B&CG, the one that has my attention in particular is the Magic the Gathering proposal. Another, which has established a 100% commitment level and is being prepared for beta is the Game of Go.
What is to the point is that there are large audiences for these topics, and bringing more of that traffic here with quality Q&A seems to fit with the stated goals of the Stack Exchange network.
Thanks for your time.