I doubt Mason will get the FA Cup final this season for 2 reasons - he has already done the League Cup final this season, and a quick check of Soccerbase tells me it has been nearly 7 years since he refereed any sort of match between 2 of the big 6 teams - and we know that the final is guaranteed to be between 2 of the big 6 this year.
I am hoping it might go to someone who has done it before on the basis that there will be no crowd, so it will be a very muted occasion compared to normal.