If only there was an opportunity to do that in England 😉
All referees in A and B are full time, so make it one list. Then there is no big thing of trial games, who is used as 4ths or those used as VAR, just a fluid list with the top performers getting the games that matter.
How would it work financially though?
I believe SG1 are paid more than SG2, so are you going to increase the earnings of everyone on SG2, even those unlikely to get near refereeing Premier League games (such as Woolmer perhaps), or do you keep SG2 officials at their current salary, in which case what's to stop them not increasing the salary of those who become PL regulars?
I'm not saying it could never work but sure it would have to be considered very careful, including the budget and HR implications.