Is bluetooth connectivity truly the only option for androids? USB adapters can are freely available on eBay and elsewhere that allow direct connection of USB keyboards, mice and thumbdrives to android phones. I would think that current ECMSPY cables could therefore be used to connect directly between the ECM and the android.
Personally, I would prefer cabled datalogging to minimize the chance of dropouts and corrupted data (always a risk with wireless comms). That said, I'm a gadget geek and would love to see a robust and reliable wireless tool for android tuning.
I would think programming for USB operation using already existing ECMSPY cables would be a much shorter path to developing your app. For me, the app functionality would have priority over the method of connection. Develop the app first and its feature set with full USB operation, then develop the bluetooth connection.
Just my .02. Rock on with your project! Anxious to see your progress.