I agree, and understand, but the seat map situation I described is still a useful indicator, because with all regular Y seats taken, that likely means there are some number of passengers holding tickets but no seat assignments. Further, those passengers are not elite, or they'd already have preferred seats at least, and likely EC seats if PM/DM, so they are not competing with me for any potential op-up. At the gate, it is entirely possible that there will be enough empty preferred/EC seats to give them to all seatless non-status pax and no one will need to be op-upped, but I have definitely gotten op-ups before with a seat map that looked very similar. Indeed, though a 100% assigned coach seat map could be another decent indication of possible op-ups, those op-ups would be very unlikely to go to a GM, since a fully assigned seat map means there are lots of elites on board, some share of which are likely to be PM/DM.

Fare buckets can also be useful, but again in my experience Delta is not as transparent about oversold/op-up situations in their fare buckets as some carriers are. (I think I have heard, though I may be making this up, that some carriers will even show negative numbers in fare buckets when oversold? I certainly have never seen this on Delta.) On a flight a few weeks ago where I was op-upped, the Y fare bucket and a few below it were still showing positive availability as I waited at the gate despite coach being oversold, presumably because Delta was still willing to sell tickets and op-up as necessary (and BE did go out with some empty seats).

But in any case, my question has become moot, since the cheaper KL fare disappeared while I debated.