If I may ask, would it be possible to modify the code to store the wallet on an USB Stick (OTG)?
Or do you see any problems with that?
-sf-
Someone correct me if I'm wrong, but the Android security model doesn't (I believe) extend to files saved on a USB OTG stick. That means that any app could access the wallet-protobuf file.
Although Bitcoin Wallet for Android uses good key stretching for the PIN, it's still short enough to be fairly easy to brute-force by your average PC once stolen by a malicious app. So, not a good idea....