Your chances are very slim, although admittedly you are booked in the best class to score an op-up as a non-member. Tell your uncle he is one lucky guy. The one-off op-ups happen to random folks, indeed it's not impossible....but it is highly, highly unlikely. In reality you're behind a long line of Cathay members (DM, GO and SL), staff (who are usually prioritized after GO and before OW Emeralds), OW Emeralds, etc. In reality, the only subgroup of non-CX people who have any regular chance whatsoever is OW Emeralds. And even then, their odds are pretty low. As for the rest, it's just dumb luck.

FWIW, I'm pretty sure BN is irrelevant towards op-ups for non-CX members like yourself anyway. It's just going to be based on an ad hoc decision of the ground staff for you. Sorry to throw cold water here. The only positive news is of the three classes where you can op-up from - Y, PEY and J - PEY is hands down the best chance, given the low # of seats in PEY and the fact that it has probably the lowest % of seats which are occupied by CX MPC members. For whatever reason, I think there are still significantly higher % of members sitting in Y, J and F compared to PEY. So you've got that going for you. Not much else.