[GeekyBear]

Again, using the iOS version of Google drive to back up the iPhone would back up all the photos, videos, contacts, and calendars.

All the user would need to do is sign into their new Android device with the same Google account they used to backup the iPhone.

Copying user files from iCloud Drive to Google drive (or any other cloud storage option) is likewise extremely simple.

I'm not aware of any lock in that isn't related to apps that aren't available on both platforms.