OBD II Trip Integration
 

I know that the OBD II does not allow access to the odometer, but it does give access to other mileage items. I think this could be used to help automatically pull miles into the trip end mileage. This would not require the app to always keep the correct miles, but it would at least give some automatic capability to the trips.

This could also carry over to gas entires that are done while a trip is being recorded.