Yeah I am pretty much running with the headcannon that it's mainly a imagination power kind of deal for yukkuris and the only way the "poo" stinks is because the yukkuri thinks so, but the very same poo can suddenly "not smell anymore" if the yukkuri forgets it's poo.
Not sure how longevity would work, probably another headcannon thing, I recall that in some old stories about the whole "making yukkuris "poo Slaves" ", unless aware they were eating poo, they wouldn't necessarily die off, only if they knew, the stress and despair would lead to anti yukkuritis. Only ones immune to this are the premmie yu's who just don't care and eat poo regardless of knowing there it came from.
And yeah, Memory effects is something I would be interested on theorizing about, one possibility like EasyDeibu said is that, it may slightly extend the memory span but not make it as long lasting as a normal human's memory or the usual traumatic core writting memory.
As we know, Traumatic Memories tend to linger for way longer on yukkuris, examples being all those yukkuris survivors recalling exterminations or similar events in their lives.
Also, we could be a bit more lenient with the experiment, allowing some extras like orange juice or similar supplements for yukkuris to be added to the mix of poo for the sake of making sure the yukkuri have enough nutrients.