R1b-V88: out of the Balkans and into Africa?

Late last year I tentatively suggested that R1b-PF6279/V88, also known as R1b1a2, and formerly as R1b1c, may have entered Africa from Iberia, rather than from the Near East as is generally accepted, because of its presence in an Early Neolithic sample from Iberia (see here).

This is now looking a lot more plausible due to the recent discovery that the eastern Balkans was home to Mesolithic foragers belonging to R1b-PF6279/V88 (see page 122 here and discussion here) and indeed a pre-Neolithic R1b hotspot (see Mathieson et al. 2017 and González-Fortes et al. 2017). Note also the continued absence of R1b in the growing selection of prehistoric samples from Anatolia and the Levant.

So here's a theory that I think is worth considering for the time being: R1b-V88, and perhaps even R1b, originated in an as yet unsampled Balkan population, dating to the Upper Paleolithic and ancestral to the so called Villabruna cluster (see here), that eventually contributed ancestry to all present-day Europeans, as well as many present-day Asians and, via an Iberian route, Africans. Is there any archaeological evidence for the existence of such an Upper Paleolithic group in the Balkans?