Hockey does have one thing that I think would make soccer very exciting. When a player commits a foul, he should be sent to a penalty box for five minutes. It sounds ridiculous, but this kind of thing would add a bit of uncertainty to the game and require additional strategy on the part of both teams when the game is played under "penalty time."
I would agree if the box time were limited to yellow card fouls. Maybe set up different rules for fouls, identifying which would result in penalty time. That would be interesting.
Players are tossed for red cards anyway (and for 2 yellows in the same game). Putting a player in the box for every foul would really stop the flow of the game.