Massey-Ellis has worked with Chris Kavanagh (3 times over Christmas for example) so if she were appointed I wonder if it would be in Kavanagh's team. On seniority, I guess Pawson is more likely for the CF though. I think Hatzidakis has also worked with CK a fair bit, but as you say Whistleblower, he's already had the honour in 2019.
So, the 'regular' teams can't always apply in FACFs as AR's may already have featured. For example, Oliver's 2 regular ARs had already had the Final when he refereed in 2018.