Paid upgrade from MFU'd WTP to F (now seems possible...)
I didn't think this was possible until this morning...
Just changing my seat in a recently MFU'd LHR-DXB-LHR T-class booking when I noticed the "Upgrade with Cash" option wasn't greyed out. Clicking it, I was able to upgrade from CW to F for the princely sum of £1,994. Before MFUing, I had been offered WTP to CW for £399 one way.
Not the best deal ever! However, I thought I would flag it as I for one have been in a situation in the past where I would have welcomed the option to further upgrade an MFU with cash... ^