A mileage program which has long been overlooked but is an SPG partner is VA.
I was having some fun with their search feature and noticed you can book SQ J seats with VA that otherwise are usually restricted only to KF members. Better yet there is no YQ! Search for example SFO-ICN on sept 5th, you'll see SQ has seats in J and F, other partners have no seats on on this flight. However VA can book the J seat with no YQ.
You cannot book SQ F though.
In other news Delta flights are now bookable online. Previously this required PUTPAC. Their rates for Short haul are better then using DL itself.
VA recently raised rates for DL but lowered them for SQ.
You cannot mix carriers or classes on a single ticket.