I'll keep this one short, because I'm not in favor of rule changes unless there's a really good reason. Messing with the rules just for the sake of messing with the rules will destroy any sport. Notice how NFL viewership is sinking like a stone? The game is just different now, and not for the better. It seems weird and that's a real turnoff, especially when it's weird for no good reason.
But one thing we can do without changing the way the game is played is greatly reduce mound visits. The original purpose of mound visits was to allow the manager or pitching coach to discuss strategy or technique with the pitcher. But now, the primary use of mound visits is to stall for time.
So my suggestion is to strictly limit mound visits. The manager (or coach) may not visit a relief pitcher on the mound without changing pitchers unless the reliever has pitched a complete inning. The manager may not visit a pitcher on the mound without changing pitchers more than than twice per game, period.
To take this farther, have the umpire jog out to the mound along with the catcher, whenever the catcher visits the mound. If the umpire judges that the purpose of the conversation is not a bona fide discussion of strategy but instead is primarily for purposes of stalling, a ball shall be called, and if the catcher does not return to the catcher's box, a walk shall be issued.
To take this farther, don't allow managers to visit the mound at all. Put a headset there next to the rosin bag, and if they want to discuss strategy, have the manager push a button to call the pitcher rather than jogging out.
I don't actually think reducing warmup pitches would help much. This would cut down on commercial break time and so it's not realistic.
Also, no manager or coach may venture onto the field of play for any reason unless dressed in their team's uniform. If Craig Counsell wants to wear his hoodie, he has to stay in the dugout.