I've struck out recently trying to get MQM's after being interlined away from DL. Every DL phone rep. I've encountered adopts the "don't fly 'em; don't get 'em" stance. Then they just up and gift me 15K MQM's (Not complaining )
Upgrades? Although interlines (at least IME) book into "Y", it's not full fare "Y", so upgrades don't happen with the full fare "Y" automatic upgrade policy that most carriers seem to have. And I personally haven't seen an interlining airline arrange an "F" seat from a coach ticket in some time. They typically assume just getting you there on another airline was sufficient.