1Ks on Y, B, and M fares are waitlisted for an upgrade to PN class ("complimentary instant upgrade" - different from the CPU benefit as it can clear at any time at or after booking). Because PN is higher than R, this is a superior upgrade request to any non-GS instrument upgrade, and you will be ahead of all upgrade requests except those of GS members.

Best case applying an RPU does nothing, worst case it bumps you down from 1K/M/WBPN to 1K/M/WBR, which admittedly is not going to be very far down the list since the only people you fall below would be anyone of lower fare or status being sponsored by a GS instrument.