Sam2 thank you a lot. Actually I heard they also prepared and ate acorn bread all over Europe in bad times and during famines, but that it’s very bitter and the tannines have unpleasant side-effect. Naturally this put me off when I first heard about the native americans acorn bread, but I was told that tannin content varies and is typically lower in american species than in european ones, and most important this is why the acorns must be soaked for weeks in a bucket, sort of like olives. Then they are ground and the flour can be used. I have never eaten, but I am told that it’s not disgusting and not bitter at all, but not very good either. I don’t think I would be very interested in acorn bread year-round and much less on Pesach, but the question is interesting. I think that if anyone was eating acorn bread on Pesach, the situation must have been bad and likely, bad enough that kitniyot were allowed for everyone.
With quinoa I see various problems. First, we need to avoid grain seeds, and that is bad enough but I think by checking carefully is solved. The second and to me much more worrisome is that we have no clue if we have dust which contains chometz and/or grain flour (even worse, because we’d create chometz during Pesach while cooking the quinoa) and the Sefaradi method to check it, is a problem, because with rice or lentils etc. the three checks are good to ensure we only pick the rice seeds and leave any dust behind, but how to do that with tiny quinoa seeds? We have to take a handful and no matter how careful we are, I don’t think this is a reliable check. This problem I think can be overcome only by certified quinoa that has been nowhere near grain or chometz, and it should be certified by someone very trustworthy. At this point for Sefaradim it’s fair enough, but it seems to me it’s not trivially permissible to Askhenazim arguing that it’s new; exactly because it’s new, most people don’t have a minhag of eating it and need to rely on authoritative opinions, but it takes time and it takes consensus. May be we can also consider how long it took from cocoa and coffee becoming known, to them being considered KLP.