It isn't on shaky grounds: you protect your private device from everyone, not just from some "law enforcement". If you want to protect your private device from any party (e.g. thieves, trivially), it will also be protected against law enforcement agents as a side effect.
And remember that the context here is you explaining your digital booby trap to a judge who thinks you might have deliberately destroyed evidence.
"Wipe the data after a number of failed logon attempts".
I understand that this does not fit completely with the "in front of law enforcement" idea, but it opposes your «any solution that starts with "setup a trigger that wipes a device" [would be] already on shaky grounds»: we can very legitimately setup triggers that wipe devices in the possibility that the device falls into random hands.