The only upgrades that I have ever had are likely for operational reasons (seat problems), or flight oversold perhaps and LUCK!!!!!!!
I have been ugraded twice to J from Y and twice to PE to from Y.
one ugrade to J from Y happened with Korean some time ago, and recently was upgraded to PE from Y on the BNE-LAX flight.
BOTH times I was unexpectedly early at the airport as the flight was significantly delayed but I was connecting and wasn't able to be told, I guess I was the very first to check in on oversold Y flights.
I got upgrade to J from Y from SIN-LHR simply because my boarding pass could not be read (originally printed in PQQ) and I guess the flight was full and the only way to reissue the pass was to find the next free seat - happened to be in J.
The last upgrade that I got was from SIN-SYD from Y to PE, they called the names of a few of us at the SIN J lounge and upgraded us all at the same time, could be a last minute booking from a volley ball team, who knows.
MORAL of story, if you want a free upgrade, likely get to the airport at least 30 minutes before official ticketing begins and you might be lucky to get an operation upgrade and hope that not too many QFF's with higher status are on the flight.