I'm not dietrichepp, but that's the gist of it. Look into how multiplexers are actually implemented, and it becomes painfully obvious that hardware cannot magic

I'm not dietrichepp, but that's the gist of it. Look into how multiplexers are actually implemented, and it becomes painfully obvious that hardware cannot magically solve your problems. And the "even if we don't get register speed" already applies today. In a sense, your system does have one large multiplexer to access all of memory. It's called the memory controller. The point is that this is painfully slow and far from register speed, so caches are built on top of it to make it faster. The same applies to disk access.