Here's what i make of it.
The ball crossing the line is a factual thing, it either has, or it hasn't, no two ways about it, that's why Hawkeye can be introduced. I can only assume if hte ref suspects the ball may have crossed the line he would stop the game when the ball is in a neutral-ish area.
Secondly;
Free kicks and penalties are all open to interpretation, this is what created pub talk and whatnot, you need to have decisions made, it's all about talking points, if every decision was perfect, football wouldn't be what it is to be honest. Each referee might have a different view on a decision Hawkeye or whatever can't be used to determine the decision of a free kick or tackle.
One is fact, one is interpretation.
Yes to goalline, as that is majorly important and a factual part of the game.
No to any other decisions, as much as it is very important, each referee is different and what would be the 5th official may not agree with the referee etc.