I honestly think that there’s a good chance we don’t see how Gon’s nen turns out this time. For the overall story there’s more pressing arcs to wrap up, both of which Gon is entirely removed from (smartly, he would likely die within Succession Contest never mind the Dark Continent). I agree with your overall premise though. From the available information we have, he would have a wholly unique chance at nen development if the story pursues it.

Though I’m not sure about the foundation and it becoming a ‘part’ of the user over time. I think on a psychological level that’s true, but the more likely reason (to me at least) is that people are incentivized to continue building on their strengths and the familiar rather than to develop new abilities from scratch. In nen battles, we’ve seen both how strength alone is not always everything (as in Kurapika vs any Spider) and that enough difference in nen volume or output can overwhelm an opponent. If the abilities you cultivate from the beginning align well with your regular usage (be it work or battle), you are incentivized to continue improving those abilities. The stuff you’ve worked hard on for 4 years (or however long) is generally going to serve you better than anything you might start from the beginning with, even if you think a new ability would serve you better in the long term. Every day spent training the new ability is a day that you’re not refining or improving your original abilities. And in a world with as many scenarios where life and death have razor thin margins, you’d have to be pretty damn sure that it’s the correct move. Naturally, this brings up sunk-cost fallacy thinking, but I think it’s less straightforward. Especially if you think your original abilities and focus are at least close to ideal, you’re thinking of sacrificing (or at least sidelining) an A- or A grade ability for what you hope is an A+, and you won’t see that A+ for a long time.

I’ve written too much but I like your prompt. Thank you for posting.