that that the widespread concept of ogres, trolls, little people, etc., could have resulted from a faint folk memory of a time when different species/sub-species of hominids lived contemporaneously?
Zero.
Humanity is quite diverse right now. no folk memory needed. We have pygmy's (short and squat - dwarflike) living next door to Zulus (tall and gangly - elflike). etc.
In a couple of hundred year we will be even more diversified. Adapting to low gravity planets like Mars and the Moon. And to to space habitats of all kinds. Maybe feet will become more hand-like to move around easier in free fall areas.
Doesn't seem very likely to me. It's an interesting idea, but how would such stories have survived, over such a long time, from before we were even evolved into the form we are now? And why would the stories have morphed into the peculiar forms we know today? While I suppose it's possible, I don't see why it would be necessary to propose this idea, to explain the folk stories we have. I see no reason to think it's any less likely that the stories could be made up without being based on any actual contact between human and non-human (but humanoid) species.
Harry, We don't know what was there through the millennia. Only a minute fragment of what has ever existed has left discernable traces for us to find. You might ask, how many tons of animal life succumbs each year, and year after year, in your neck of the woods, and, except for occasional road kill, is never noticed nor ever seen again. The Denisovan strain of the Homo line was unknown before 2010 - and then only from a few teeth. What is claimed to be a Denisovan leg bone has since been found - but it was found thousands of miles away from where the teeth were found. Genetic markers of the Denisovan line have since been identified in modern humans, as have Neanderthal markers - and they had to be there all along but unrecognised for what they were. Evidence of a further, entirely unknown and still unidentified, human progenitor strain has also been located in modern man. Without any known remains having yet been found, science is still pondering that one. The diminutive, so called, 'Hobbit' population of Hominids of the island of Flores, was unknown before the start of this decade. Thought is that this species of human went extinct 50,000 years ago. It, or something like it, has long been reported by local people - possibly just lucky, persistent over the generations, intuitive guesswork to no particular purpose. Of course the famous 'Lucy' and her kind were also very small (and long armed).
I think there is plenty of possibility for pockets of earlier, different, Hominid types to have imprinted in the psyche and perpetuated in folk memory or genetic memory. The Neanderthals seem to have been ugly, stocky caricatures of Homo Sapiens. For all we know they had knowledge in some areas that surpassed that of contemporary modern humans, they were certainly stronger than us, making them seem even more frighteningly different. I don't see any reason to compare an artist's rendering of an ogre in a modern children's book, or even one from 10,000 years ago if there could have been such a thing, directly to an imaginative reconstruction from Neanderthal remains and say, see, they are nothing like each other. We have no way of knowing how the various archetypal folk images have evolved over the millennia. One can only protect oneself from the possibilities by declaring to not believe in it. Just like I do for all the images of angels and cherubs and Jesus and Mary, and King Henry V of England, and Prester John, and Atlantis, and freedom and racial harmony ever being the remotest possibility in America - I just know of not a jot of credible evidence for it.
Just a few rambling thoughts Mr Demon. Thanks for your comment - much appreciated.