It's hard enough to figure out what a strike is for pitchers/batters per umpire.. now you are having dudes stand 3 - 4 - 5 - 6 feet back, trying to determine how far is too far, throwing fast balls, or standing too far to the left, too far to the right.
I feel like it would lead to an absolute nightmare. You can still get 2-4 steps back easily and get set. While using all of the options mention above. I don't see the need.
I would prefer to see bat standards continued to be evaluated and become safer as opposed to trying to move the rubber back or add a floating option.
This is my personal opinion and anyone can disagree.
As I mentioned above, it wouldn't be the end of the world if they implemented it. I just am comfortable with the current set up and feel there is no need to make a change.