Coming in a hotfix soon -- before next Tuesday -- Blizzard will make all rated battlegrounds 10v10s. This is in response to the popularity of 10v10s when compared to 15v15s. Ideally, this will also lead to increased participation in rated BGs, and we can all have an easier time at obtaining those coveted titles.
Blizzard's full statement is as follows:
We're in the process of developing a hotfix to push before next Tuesday that will change all 15vs15 rated battleground weeks into 10vs10 weeks.
Looking at participation, the 10vs10 rated battleground weeks have been far and away more popular than the 15vs15 weeks. The difference in organizational requirements as well as battleground map popularity have been a couple big factors that have led to the 10vs10 weeks seeing a great deal more action. By making this change and supporting the popular option we hope to encourage even more players and teams to participate, as they won't have to wait out every other week, or struggle to beef up to 15 players to match the requirement.
We also have plans to adapt additional battleground maps in the future to work in the 10 player bracket to increase the variety of maps available.