[AM160]

This would make an incredibly long day and reduce flexibility within Breakfast. The presenter could end up doing five hours on air. They'd presumably not be available for the daily programme meeting and have less time to input into the script. 

i think you might be overestimating how much input the presenters actually have.

Even if each presenter only does one day a week the One and extended Breakfast is certainly adding to their hours or taking them away from other activities e.g. pre recorded interviews. 

it is very very rare breakfast do pre recorded interviews (in studio)  
Any junkets or pre planned shoots are exactly that.. pre planned and tbe rota  is already worked around that.

Why can’t someone new (and local) become the main pres? Why does it have to be an existing face?