That we are exploring other computing substrates does not mean that those substrates will be economical or practical to use. They either will be or they won't (a determination which is ultimately dependent on the laws of physics). Our exploration of other substrates is a necessary but insufficient precondition to actually putting other computing substrates into production.
It's kind of silly to assume that what we have now can't be improved significantly. We've only been doing this for a very short time in the grand scheme of things. We're certainly nowhere close to hitting any limitations when it comes to the laws of physics here.
We just won't know until we get there. We have hit fundamental limits of physics for other technologies. Planes don't really go any faster today than they did 40 years ago. Cars can go faster than they did 40 years ago, but they don't in practice. We don't have flying cars. Etc.
I'm not saying that none of these other computing substrates won't work, just pointing out that the simple fact that we are exploring them does not mean that they will. Technological progress is neither guaranteed nor automatic.
I mean yes we literally don't know right now. I'm just saying given where our civilization is at, I think it's pretty safe to assume that we have a lot of room to grow here. Once we've done computing for a thousand years or so we'll be looking back at this the way we look at cavemen banging rocks together.
Seems like a decent probability outcome to me. But it also seems like a decent probability outcome that we hit the end of the line of what’s feasible with silicon lithography in the next couple of decades and computing substrate progress basically stalls out for decades or longer until some other breakthrough happens. A parallel would be the stall in progress on personal automobiles until lithium ion batteries made electrification possible in the last decade.
