There is actually 2 black (-) leads. One comes from the bottom left side of the board and the other from the 510 connection. There would be at least one long wire regardless of which way the battery case was placed.
Although I rewired every chip for reverse battery protection I felt most people are used to the + on the top so decided that would be best in my design.
The new software for the sx350 includes the ability to flip the screen (even an auto mode that uses the gravity sensor to automatically flip depending on how it's held) but turning the whole chip over puts the negitive lead coming from the board in the way of the up/down buttons as well as the screen much lower on the side so decided against that as well.
I put a lot of thought into this design and it is currently in its 14th revision which is the one I am finally satisfied with
Sometimes it's tough being OCD