Why did the DIY Drones team make the design decision to mount the GPS module on the board directly instead of using the JST type wire cable to allow external mounting of the GPS?
If the plane is made with carbon fiber shielding or other GPS signal blocking materials, it would enforce some physical constraints of where to put the APM 2.0 autopilot.
Are there plans to sell a separate SD card breakout (instead of the one with GPS module) for those who preordered the APM 2.0 and want to switch to an externally mounted GPS?
Whether or not they started with an external option is the past. The point is for those who preordered the onboard GPS APM 2.0 should have the option at least of purchasing the GPS-SD card breakout board in the store
You have to physically cut off some wire from the onboard GPS first. And then plus in an external GPS. I don't think you can pick just any GPS neither.