One class over different class return

[mrsterryn]

JAL, British Airways both seem to give the ability to have , for example, business over and premium economy return SYD LHR return .
Do many other airlines permit that ?
I vaguely remember that sometimes BA would have "buy business and have first one way " sale
Also Qantas used to permit the ability to pay extra to have the next level up for one way. Is that still a thing ?

 

[FlyingKangaroo]

I could be wrong but I feel this functionality has been "enhanced" away on several airlines I'd done this with before Covid. I'd definitely done it with Qantas several times but noticed a few months ago that the system absolutely refused to let me do it. I couldn't be bothered with the call centre roulette so I booked elsewhere.

 

[Forg]

Many years ago, when PE wasn’t as common, I did a combo thing with J between SIN & BRU and Y between SYD & SIN. It was with KLM (admittedly a 2nd-rate J at the time), and allowed me to buy a round-the-world Y trip for the better-half as well as my trip, for the same cost as me flying J the whole way.