I think we need to be clear about the "it", as in "I doubt that "it" would be possible"! When the "it" in our conversation is what I call "pure genealogy", it has to stop when the reliable documentation stops. In the domain of what I call pure genealogy, even DNA can't take us beyond reliable documentation; DNA can tell you that it's highly probable that George and John are related, but from the perspective of pure genealogy you don't actually know they are related until you can show it with documents.
The Pedigree I'm looking at has some pure genealogy in it back to 1200 or 1300, but beyond that there is no reliable documentation, so my question -- the "it" I'm talking about -- is really about the stories, not the genealogy. The Welsh bards were story tellers, and the pedigrees are part of the stories they told of ancient heroes and gods. In this pedigree the stories go back before Wales to Greece and Greek and Roman gods, and then back to biblical characters. So my question is really about the history of the stories -- how did they develop, and where did the connections between Wales, Roman Britain, ancient Greece, and biblical narratives arise?