I heard this discussed on the wireless yesterday and one idea that has been put out is similar to the tennis where players have a number of challenges. Given to a manager, and perhaps only allowed for:
Penalty Decisions
Red Card Decisions
Off the ball incidents (e.g. violent intent)
then perhaps the game would still flow. There are what, 20 odd cameras at any game and if the 4th official has a judiciary role in reviewing the video evidence, then I could see it working. It works in cricket and adds to the enjoyment on the game, also in Rugby...why is football so hallowed?
We used to have a dinosaur in charge at FIFA!!!!

I like the idea of a manager having a maximum of 3 challenges and I have always advocated that the TMO (or whatever they're going to be called) should only be used for the decisions you've mentioned above.