I think no. Just plainly no.
That would make HxH kind of a franchise. You have approved canon sidestories just like in the comic market to fill the gaps.
But HxH is not a work like that. HxH lives off the fact that one person has a very thorough idea about how that world works and who does what. It has a very distinct writing style that has not focused on fanservice or about fulfilling all expectations.
Even if we assum the amateurs only touched things togashi would never touch again, i feel it would be bothersome if it were not a one off thing like with hisoka but a regular thing.
I mean, imagine this: Togashi returns once every 1 or 2 years for ten chapters, but in the meantime, over these two years, two 1 volume oneshots (those would be 20 chapters) popped up. LEt's assume they are good and canon and togashi approved them. That means double the noncanon content than canon content came out in that given timeframe.
That is definitely going to shape or fans view HxH and it is also influencing togashi if he has to read the volumes to approve it. Some of these volumes will be popular and change interpretation of a some characters. The danger here is that the amateur volumes are going to overtake the togashi content and impact it negatively, both by influencing and possibly demotivating togashi and by making togashi's content less relevant.
AFter all, what happens if togashi wants to move away from the martial arts content (like he does in the latest arc) but there are 2 popular one shots that are just about fighting through heaven's arena? That would surely create a conflict here, as the fanbase might want togashi to create martial arts fighting content too and crave more of that rather than following the new direction togashi wants to take.
