Interesting, what if the security on the device was reduced purposely and in a manageable way, in exchange for one of the several steps or keys to decryption existing only in an online blockchain of some sort?

No, because I put the device in a faraday cage, with whatever proxies I need, crack it, then put it in a woodchipper. No one ever finds out.

Existence of such system wouldn't make much difference, because no authority would wan't to use it to access the data. They would claim that the target's inability to detect a wire is crucial to the ongoing investigation.

But what if you need the blockchain to crack it?