Connecting via Bluetooth LE
This requires Android 6 with full MIDI support! (Sadly not all vendors consider it necessary to support MIDI)
MIDI over Bluetooth LE has been de-facto standardized by Apple with OS X 10.10 (Yosemite) and iOS 8. You will see more and more compatible hardware, mainly input devices like keyboards, but also BLE to 5-Pin interfaces from Kickstarter projects as well as big name companies in the years to come. Android 6's MIDI api also supports it and TouchDAW 1.65 now makes it available as well.
There is one serious issue with this on Android, though: To be able to scan for and pair with Bluetooth LE MIDI peripherals, Android's systemwide "Location" setting must be on and the app that does the scanning and pairing needs to have permission to access a user's location info. Frankly: We are not going to ask for that permission. Not now and not any time later when more than 3% of users will be on Android 6 and might actually be able to use BLE MIDI.
Fortunately every app can use BLE MIDI peripherals once they have been found and paired, regardless of the permissions it asked for. So if you are willing to give away your location, grant permissions to another app and use that app to hook up the BLE peripheral you can still use it in TouchDAW despite its author being some stupid and overly privacy minded German.
Google are somewhat aware that the permissions needed here may be an issue. At least the man who authored Android 6's MIDI system is. He has therefore made a simple utility that hooks up BLE MIDI devices available on Google Play. Download and run it after activating "Location" in the system settings, connect your BLE device, then set MIDI connection(s) in TouchDAW to Bluetooth LE.
Notes, known issues:
Bluetooth is still weird, buggy and wildly hardware dependent on Android.
Bluetooth LE is not "faster" than traditional Bluetooth. Latency may become an issue especially with high rate DAW control traffic.
Android's MIDI api only acts in "central" mode. It can not be a peripheral to other "centrals". To connect to a Mac, the Mac must advertise its services. It will not see the Android device.
Don't let anything go to sleep. If you do, you may end up with a dead MIDI connection and no way to break and reestablish the pairing.