I'd rather see them allow substitutions and keep playing the same sport.
In any event, someone will eventually score. Fatigue becomes a part of the game and you deal with it. Not decide "this is too hard" and go have a kicking contest.
SD
When you start allowing rolling subs you completely change the nature of the contest and probably wreck smaller nations/teams chances of doing well because big established countries or rich clubs can just field more decent players.
The game is fine as it is. Penalty shootouts just happen to be a quirk because no better tie breaker has been thought of. Youre going on about them as if they decide every single match.
Anyway Ill say it again. Theres no tension like a penalty shoot out in sport, if its your dog in the fight. They might not be ideal but theyre entertaining, in a masochistic kind of way.