Taking this to an extreme, the whole idea of a TLB sounds like hardware protection too?

As a thought experiment, imagine an extremely simple ISA and memory interface where you would do address translation or even cache management in software if you needed it... the different cache tiers could just be different NUMA zones that you manage yourself.

You might end up with something that looks more like a GPU or super-ultra-hyper-threading to get throughput masking the latency of software-defined memory addressing and caching?