My personal opinion is that it was majority I at least back to maybe 3000 BC. Of course, in the time window of it's emergence and 3000 BC, Hg I probably lived somewhere in Asia near Fertile Crescent.
As I recall, we have couple of hundred skeletons from Lepenski Vir, Vinca and Starcevo cultures, but there is still not much people here interested in those kind of research. I guess that prices of carbon dating and DNA analysis are way off the reasonable limit for current Balkan standards, so they don't even think about it. I know that EU is funding a lot of science projects here, and some are done in collaboration with students/colleagues from abroad. It's evident that more relevant research will be done in next 10 years and we will have definite results about DNA structure of Balkans BC, which will help us reconstruct the past events.
Lepenski Vir DNA would be very interesting.