Two comments.

First, more important, to me, than which side operates which brake, is which brake I use on which bike. For instance, on a road bike I use the front brake much more than the rear brake. Hard braking with the rear brake only slides the rear tire, causing excess tread wear, and doesn't do much to slow the bicycle. However, when on my trail bike where it is much easier to slide a tire, I use the rear brake because I want the rear to dig in and slide. I can control that with the steering. A sliding front usually leads to a crash (been there, done that).

Second, the safety issues associated with being able to brake, in a corner, with only one hand (left or right) on the handle bars seem pretty scary. Doesn't matter which hand has a tight grip on which brake lever -- if you have to brake hard you are toast either way.