i would ask for an upgrade.
chances are if cx gave you one, it would be a space available and confirmable at a time that was close to departure.

if they gave you a jto f (d to a) upgrade you are still flying on a premium ticket. its the y to j upgrades that de-value the premium product. if cx played their cards right and made this upgrade a >24 hour upgrade they would be giving you a seat that would probably go empty and keep you as a happy (premium paying) customer

just my 2 cents