i've always wondered if there could be a cryptographic solution to this. issuing decryption keys to governments seems rife for abuse, but some sort of multi-party situation where governmental and non-governmental entities have to cooperate (with actual multiparty key material) to perform a decryption authorized by warrants- with said non-governmental agencies acting as a check on usage of those warrants, their frequency and the eventual publication of their usage could be an interesting approach.

personally i think strong encryption should be a requirement for digital evidence, but even that can be forged.

strange times we live in.