Well, I posted about this before elsewhere, but I was recently on a EWR-SLC flight. There were 6 of us on the upgrade standby list; me as a Platinum I was #4 and my non-elite companion was #5. So only one other person on the list below me.

But when they called elite boarding, a mob of people approached the gate. I know at least one was a DL elite (saw the BP), so not eligible for an upgrade, but I think for whatever reason, the upgrade standby list is NOT necessarily a good indicator of how many elites on the flight.

But I think it's moot anyway, my sense is the original poster wants to get this information well in advance so as to try and book a flight that has fewer elites, with the goal of increasing the odds of an upgrade. I don't think this information would really be that useful anyway, because you'd have no control over how many elites book the flight after you.