I've done some digging into DC/DC converters and have narrowed in on some TI step-down regulators that I'm going to play around with for integrating 2 regulator circuits on the board to be able to power everything from a single 11V-15V battery. Trying to cram two of these circuits onto the board while it's already full is going to be a fun puzzle! I've been trying to keep the I/O pins inside the edge of the HAT but I'll likely have to abandon that goal and I'll also be eliminating the ftdi header to create much more room; the FTDI header takes up about the same footprint as one of these circuits.

The reason I'm trying to embed 2 circuits is to have a completely isolated supply to provide 5V for the servo header. Each circuit will be able to provide 5V at 3A.