The issue is, although it is one of their users accounts you don't know if it is an active account or if the e-mail address that's attached to the account is still active and good.
But this situation could in fact help OP with the case.
Correct me if wrong. But considering the situation OP is in, if the owner of that Address has not logged on to KuCoin for over an year then the Exchange could send out a notification through Email or other methods of communication to the owner. Something like a deadline 12 months for now. If the owner never responds and never logs back to KuCoin either, the Coins be returned to OP.
In fact. I believe most Exchanges have this clause in the Terms where if you do not log in for a particular amount of time, they reserve the rights to claim your funds.
I do not have a better idea than this, and even mine could be very stupid. Anyway. I do not think KuCoin would bother with a complicated situation like this. Exchanges barely bother with much simpler situations, let alone this one.
But maybe there is hope for a shine at the end of the tunnel. Who knows. OP can only hope.