Most airlines tend to use fairly complex, unreadable and ultimately hard-to-guess/understand systems. The only exceptions tend to be US airlines which tend to have a more simple and publicised mode of operation. For QR, a number of official elements may come into play, including operational incidents, fare paid, frequent flyer status on QR's own system (probably very little emphasis on status with OW partners) and more.

It is also not unlikely that unofficial elements might well trump all else (e.g. I would not like to be in competition with someone from an influent family if they could only confirm their 4 year old son in Y wit the nanny and want him upgraded).

Bottom line, impossible to guess, although some things are (almost) sure to deny you an upgrade (e.g. ordering special meals, travelling with numerous other people on the same PNR, etc).