Nothing new here. Basically the genetics, matches the historical accounts. We know (by historical accounts) that the slavic immigration started in the end of the 6th century, after the death of Justinian the Great, where the successors lost territories and few battles and could properly defend the frontier. (avar wars).
Also, after the Justinian plague (541–549 AD) a lot of the local population was decimated, hence the new slavic arrivals found it easier/space to move to the country side (initially as a trickle of immigration in the late 6th century, then eventually as settlers/invaders later in the early 7th century).
No, the genetic factor itself is something new here, and interesting even to this reader with an academic background in a related field. Florin Curta (a very respected scholar overall) has held out against the mainstream view of a Slavic migration into the Balkans on the basis of a supposed lack of archaeological evidence. So, I suspect that many scholars, as soon as they learn of this news about the ancient DNA, will immediately think “Hmm, I wonder what Curta has to say to that.”
Also, after the Justinian plague (541–549 AD) a lot of the local population was decimated, hence the new slavic arrivals found it easier/space to move to the country side (initially as a trickle of immigration in the late 6th century, then eventually as settlers/invaders later in the early 7th century).