I've always felt in a perfect world they should be equally accessible whether you are standing at the front or the back of the keyboard....  Nord does it better than most on their stage pianos because of no overhang off the rear above the ports.

I don't mind as much but I do like it better when the jacks are labeled on top of the keyboard so you can tell by lining up your hand with the label that you're plugging in the right stuff.  I usually feel the back and count jacks but I don't always remember if A/D inputs are first or where the headphone jack among the rest.   

Yamaha MO6 had these high contrast labels which were helpful: