One would hope that with the proliferation of two-class RJs, and the advancement of hand-held technology, flight attendants at the mainline and regional operators would eventually be able to sell that passenger an upgrade or communicate with the gate agents to sell that passenger an upgrade.

Easy solution would have been for the FA to let the passenger go back to the podium and buy an upgrade even though the FA said "they weren't supposed to let them do that."

Most of us already have mileage-earning credit cards, so that sales pitch is useless for many of us, but upgrades into empty seats are something that everyone might buy again and again (any flight where they see an empty seat and a POS/COS squeezing them in their steerage seat).