Again, as a thought experiment, what legal protections can we put in place - an encryption ombudsman or independent authority - that would allow an arms length,

Again, as a thought experiment, what legal protections can we put in place - an encryption ombudsman or independent authority - that would allow an arms length, controlled and expiring mechanism that allows limited access to a user's data? What would we as a society be happy to accept? I don't think the demand is an unreasonable one, but I'm trying to figure out what a reasonable collection of mechanisms looks like.