QF do not sell WT+ as a codeshare. You can only buy a QF codeshare ticket in WT, CW or F. Until recently, you could not buy QF in J on BA since their J products were quite different until QF installed the skybeds.
BA used to allow on-board upgrades by paying some large number of pounds. I am not sure if they will permit that with a QF codeshare ticket. However, if they still do on-board paid upgrades, I can't see why they would be concerned if you were on QF or BA ticket.
So the question is whether BA still do on-board paid upgrades?