In a hundred years, will any of the stuff in Arc matter? What exactly? The innovation in Arc is minimal, Clojure does much more in new and better ways.

concurrent high-performance immutable data sounds pretty much like the fabric of reality. So I would hazard a YES :) In fact it'll probably matter in a million years from now.

"Multi-core is here to stay", says Rich Hickey

Hopefully not. Multi-core should be seen as a stepping stone on the way to better technology.

Why not have multi-core version of other tech, unless you are talking Quantum Computing, though isn't that in some ways the ultimate form of multi-core?