Nice thought. The problem is that turning your iPhone off is the easiest way to secure it quickly and completely. Whether it's an overbearing TSA agent or police pullover -- if you want your data to be secure (password protected vs fingerprint protected) you can always just turn off.

Anything iCloud-initiated does not benefit from the protection of the secure enclave on the device--so with your idea, you'd be opening a denial-of-privacy attack vector