Would be good for U23 players and fringe, but the top clubs simply don't want the extra fixtures.
yes and no.
for Liverpool to win FA cup they had to go through 6 games against Shrewsbury Town, Cardiff City, Norwich City, Nottingham Forest, Man City and Chelsea. Out of the 6 games, in the first 4 Klopp was able to experiment and give playing time to reserves and youngsters, because 3 were lower league sides and 1 was on their way back to lower leagues. His best player Salah wasn't even called up for those first 4 and played 123 minutes in total.
for Juventus to get to the Coppa Italia final we had to go through 5 games, playing Sampdoria, Sassuolo, Fiorentina twice and Inter in the final. The Coppa Italia format almost guarantees these sort of opponents, it's almost impossible for lower leagues to reach the rounds we start to play in and in result we hardly rested our first stringers. f.e. our best player Cuadrado (at least imo

) started 3 out of 5 games and played 340 minutes in total.
I'd much rather have the FA Cup format, for me it's a lot more entertaining having these David vs Goliath matchups and seeing younger players in action. Current Coppa Italia format for top clubs is basically additional 5 Serie A rounds that are packaged differently.