Scoop from my latest flight, though one completely clueless crew member might not have been entirely sure what he was talking about.

I was looking at the manifest and they have a list of miles for each member, and miles required to upgrade. That included Y - J, J - F and also Y - F. According to the crew, it is possible to do a Y - F upgrade on a 3 class flight using double the miles (so 65,000 miles instead of 32,500 for a Flex ticket on DXB - SIN).

I thought this was interesting as I previously thought this to be impossible.