Interesting subject....
I have to say I agree with M.Mouse.
In my company we carry alternate fuel, final reserve fuel and an extra amount of fuel, depending on flight number, with minimum 15 minutes. This extra fuel is a statisctically found number. The company monitors all flights and per flightnumber it is then decided how much extra is enough. This works very well. For instance, most flights to LHR carry about 25 minutes extra.
In this scenario a sudden runway closure or bomb thread on the tower is not catered for.
Nor should we cater for that, IMHO. Thing is, if you have to divert, TAKE THE DECISION. Don`t wait for all eternity in the stack untill there`s no alternative.
If your EAT is way past your limit, call it a day and carry the consequences of the fuelpolicy. Don`t let it become a safety issue.
Generally speaking, I take more than flightplan fuel in only 5 percent of the flights. I cannot recall the last time I actually needed it.
No, I`m not trying to brownnose myself behind a desk.