I have created a website for the K1a2c haplogroup, which was introduced with the publication of Behar's paper in 2012. It is defined by coding region mutations T4216C and G7775A. It is estimated to be between 5,000 and 13,000 years old. There aren't yet any descendant clades identified for it. I don't know how many FTDNA customers belong to K1a2c or how common it is in the general population, but out of a total of over 2,000 members in the Haplogroup K project who have tested at least HVR1 and HVR2, around ten or roughly half a percent have been assigned to the K1a2c group, with or without recognition by FTDNA (one HVR1 mutation, T16288C, seems to be common in this subclade, thus allowing prediction of K1a2c also for some of those who haven't tested the coding region). A few K1a2c members have identified their most distant known matrilineal ancestors, and based on those I think we can see a pattern pointing towards a northern European origin, somewhere near the Baltic Sea. We would however need more samples with researched ancestries to have this origin confirmed.