Currently, the min version supported by the app is 4.0:
Android 4.0 (and older) are used by a residual amount of users:
https://developer.android.com/about/dashboards/
We can not forget that there are also some features not supported for such version, f.ex. the ones that take advantage of the Jobs (available from API 21).
Since Android 4.4 keeps ~7% , it is a possibility of minSdkVersion. Other option is going directly to 5.0
Your ideas are welcome