Not to derail the thread, but the Refs really need to spend more time honing their craft.
There's a great expose on a college level ref (could be lower, don't quote me on that) that opened a facility or program (can't remember which, maybe both) that trains refs and prepares them to be a more competent workforce. I'm sure it's still going on, and if it's not...that's a damn shame. It was a good idea, that I think all parties involved can benefit from.
Anyway, back to the judgement calls on PI. I think it would work IF, all judgement calls were reviewed. Let's face it, taking a few minutes to double check a call isn't going to hurt anyone. It's not liek they have to look that closely at slight movement of footballs, or tip toes stay in bounds. I think checking for PI would be pretty damn obvious, and wouldn't take tat long at all.
Maybe refs should carry some kind of tablet or smart phone device that they can receive video on (from upstairs or the sidelines). make it capable of zooming in real quick, and bam...they can group up on the field, look it over, and get on with the announcement and game.
Pipe Dreams.