It looks like the Pololu is the clear favorite so far. I spent some time thinking about phasing the current board out. The Pololu drivers are nice, but they are not for everyone. Some people may want higher resolution and some people might want more power for a larger or heavier machine from Gecko type drivers.
Since the Pololu drivers plug into the board, this allows a few options. A small daughter board could be placed on the header connectors. These connectors have all the essentials like the step and direction signals, motor enable and +5V/+3V.
The schmitt trigger does not have much output power (5.2mA). I was worried if they could power opto isolated drivers. I talked to Gecko and the G540 only pulls about 1mA per pin, so that one will fine.
The Keling style drivers probably pull more based on the schematic they give. I tried to find a stronger schmitt trigger, without much luck. The one I use is a non inverting type which are less popular. Then I remembered that many of the opto isolated Keling style drivers use inverted logic. I can get an inverting schmitt trigger with the same pinout that will do 25-30mA. The 3 stepper terminal blocks already on the board could probably be used for the keling drivers by rerouting the signals via daughter card.
The new board board also has the relay drivers and PWM/Pot power mode, so it sounds like the clear way to go. I sent an email to Pololu to see what my options were for selling them directly
Thanks for all the input.