The presentation
“Lessons from Incidents & Accidents” gives instances of the problem of inadvertent brake application during takeoff.
Although the concluding recommendation is for ‘feet down’ for takeoff, this might be better worded as heels on the floor, but with feet ready to input rudder or brakes as required.
An issue often overlooked when changing SOPs is that the design and certification requirements may have made assumptions about foot positioning to control the swing from an engine failure, or applying brakes during an RTO. A change of SOP could invalidate these assumptions and thus result in reduced performance.