What needs to be said Notso Fantastic is you must either be very unfamiliar with your aircraft or it is not of a particularly good design. The certification regulations provide ample protection against inadvertent rudder input during take off or landing in a crosswind. Thus you overrate the problem of brake application during takeoff.
The problem of heels on the floor is not only the time it takes to move the feet, but also that the feet are not moved. In time of stress (RTO) we forget – human error.
The RTO training guide is based on accident evidence where crew have attempted to apply full brake by rotating the ankles with the heels still on the floor; in most aircraft types this is very difficult if not impossible. Furthermore when the rudder is only adjusted to enable full travel with the feet on the bar, then you may not get full travel when attempting to brake i.e. crosswind RTO double trouble. Follow the manufactures / industry advice.