Anish references the six referee rule that Michel Platini has implemented for the Europa Cup and already David Moyes is irate because he believes that the goal line assistants missed a deliberate foul on Louis Saha by AEK’s Juanfran which got the Everton striker sent off as he retaliated.
So why is it not going to work:

The Parallax error. More on it.
The problem of parallax:
Having six referees should minimize parallax error. But it is no given. The orientation and the direction of the referees have to be right and who is to say they were wrong in the first place because parallax is so subjective.

For an explanation of this image, go here
The persistence of vision:
There is a reason moving picture technology works. The brain is limited by the number of images it can process and the human eye’s capacity to retain an image fades in about 1/25th of an second. This “virtual memory” is limited and the world moves a whole lot faster than that. The two additional linesman patrol behind the goal where the action takes place and the referees then discuss through radio link what they saw. In the end the referee has to collate all this data and come up with the verdict. There are so many levels of corruption that it becomes a sort of Chinese whispers.
More bodies to direct fan anger at:
Not getting a foul right or awarding an offside goal can potentially lead to physical harm to linesman patrolling the more circumscribed goal space. These linesman may not have anything to do with the ultimate decision but they could become the first targets of fan wrath.
There is already existing video technology which is cheaper and more effective. The purists had a problem with maintaining match continuity but from the looks of it the additional linesman are going to be equally disruptive as referees consult through radio and on the pitch and after all that still not get it right. I keep thinking of the bad tempered days of John McEnroe and Andre Agassi who were terrors to the line judges and referees. The introduction of Hawkeye has changed all that leavening tempers and focusing on match performances. Although with Serena Williams all bets are off the table.