It might work if your fingerprint was used while you were unconscious, but any solution that starts with "setup a trigger that wipes a device" is already on shaky grounds.
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.
There are videos on youtube where the lawyers tell you what your rights are at traffic stops, also there are ones that talk about the different rules when coming through immigration. These can be painful to see when they show the ones where cops ignore limits.
So at the border, they tell you that you are legally required to provide your finger print, you do that, and don't say a word. I'm sure it will be a bad day for you, regardless of how it works out after years of litigation on whether it is your duty to tell them how NOT to unlock your device.