I have a board with a mix of voltages. It wound up being one voltage to one side of the board, and one to the other. I'd like to make this board 4 layers instead of the original 2. Is there any reason I shouldn't split the internal +ve voltage plane into two? A 3.3 VDC on the left and a 12 VDC on the right on a single internal layer? I'd keep a single ground layer for all.
I don't immediately see an issue with this and it would save cost from needing 5+ layers.