>But it's not the hardware that's the difficult problem

I think the problem is that we're still making the distinction between hardware and software. There isn't any. Or if we insist on it we have to deal with the von Neumann bottleneck.

Hardware-software hasn't been cracked yet. I believe this is a good primer on the issue: https://youtu.be/0UVa7cQo20U

From what I can understand, current hardware and software paradigm is the limiting factor.