Originally Posted by ernestnywang

I don't recall this topic being thoroughly discussed, but my guess is that it was simply too complicated. Back in the old days, they issued paper-based MCO on 160 (CX) stock to be applied on the 125 (BA) stock ticket. There's a different record locator for the upgraded segment and all is good. Now, with e-tickets and PNR matching the e-tickets, as well as married segment and a lot of other things, it was probably too time-consuming to process these BA and AA upgrade requests. That's probably why CX stopped offering them.

I agree the T class-to-U class upgrade on BA was a bargain, especially given CX does not allow E class-to-U class upgrade. On the other hand, neither BAEC nor AAdvantage members could redeem CX upgrades, so it was a bit unfair, or at least not reciprocated.