I was on an SFO-MSP flights a couple of weeks ago and the gate display was offering FC upgrades for $150 prior to the upgrade list being processed. I pointed this out to the gate agent who said it was a mistake and quickly removed the upgrade offer from the display rotation.

As to the OP's statement, I'd say it's somewhat of an open question as to whether the "math" favors a 'T' fare Diamond over a lower status flyer who often flies on K+ fares. With the coming revenue requirements, DL may have a different opinion.