I'm stupefied about some of the nonsense that has been written on this thread.
Airbus have made many comments at instructor symposiums that they purposefully stay out of this debate. The books are silent, and will continue to remain silent on this issue.
If you have soft rubber shoes, feet on the floor can actually jam the rudder pedals. So, some companies dictate the types of shoes you wear. Others insist that with feet dragging/scraping a bit on the floor gives you more feel for fine rudder inputs. Also that for an RTO, you might inadvertently disconnect the auto brake.
There is also plenty of Airbus pilots who feel that it's the only control where you can feel what the other guy is doing. I want to know exactly what the other guys is doing, so you won't find my heals on the floor ever.
5 years on type now, and only once has someone squealed to me during a TO roll about my feet. That same person has also been fired from every company he has ever worked for, CRM being the major issue.
I think Airbus has a point, stay out of it. If someone want's the other way, deal with it. There's no right or wrong.