That's awesome!!! Definitely need some positive articles out in circulation about tickling, all you ever see are the ones about how evil it is, or 'never do this,' or how much people hate it. Always sort of depressing to see so many missing the point of what it could be.
Sadly I have like 0 memories of childhood (well, like 1 or 2) so can't really contribute in that way.
I would add that there are established medical benefits of laughter that the Lee gets in a consensual experience. Endorphins and Dopamine are released, stress hormones like adrenaline and epinephrine are directly countered, relaxation can occur, heck you even burn calories, all of that comes together to suggest that tickling is this beautifully adapted mechanism to draw directly from the wellspring of benefits of laughter. Though it must be consensual as anything forced will directly generate the sort of stress hormones that safe laughter normally addresses, and probably make things worse in general. The Ler gets some of these benefits as well through the smiling and sympathetic laughter they exhibit.
All the theories are that ticklishness is a throwback instinct to learn to avoid danger, or to show submission to someone attacking you (from the articles I've read) seems to me it is more a biological defense mechanism in a world that is increasingly harsh, stressful, and driving people crazy with the sort of "never stop running" mentality that is so abysmally unhealthy for us as human beings. It's a marvelous way that humans have at their disposal of coping with all of the insanity of life, and I'd suggest that most cases of people "hating" tickling/being tickled are those with traumatic experiences in their past, "friends" and bullies taking it too far and not respecting the boundary of when to stop. So for these folks, tickling will always be tainted as a torment used to deny them agency in their own life, unless they actively take steps to mitigate the harms of the past in order to benefit from this lovely stress defense mechanism we all have.
As far as hardwired, that's hard to say. There is still a lot unknown in the psychology world about the formulation of fetishes, it could well be hardwired, but one theory I've heard is that its a development of coincidence, in a moment of sexual self play, something unexpected happens, ie you find yourself being tickled or watching someone be tickled, and the brain forges a connection between the two. As far as I know. Its all still theory of course.
Can't wait to see the article, best of luck!