Cost aside, I would like to know just how every household where there is a school aged child or a teacher is going to be able to access a holiday when suddenly you only have the choice of going in a six week period over the summer.
For one, many departments of perfectly ordinary, every day public services (doesnt have to be military or police, many hospitals or customer services work this way too)are run according to strict staffing numbers. If most of those employees have school age children they are all going to be wanting to take their annual leave in this 6 week period. Can you imagine the scrum for annual leave? Where both parents work then you can double this problem.
For another, there will simply not be enough flights/holidays to go round everyone, even if people could afford the inevitable hoik in prices. You would have to book 2 years ahead for both annual leave and holiday itself which isn't doable.
Finally, I don't want to see businesses and employees in family holiday resorts suffering because they are lying virtually empty during term time. They probably wouldn't be able to operate going from one extreme of demand to the other.
Altogether a ridiculous idea and I work term time in a school myself but don't lie with the "I have to do it so you should too" brigade.