Others may disagree here, but I don't think Arc was really intended to contain new concepts. The phrasing of "Hundred Year Language" was I think a nod to timelessness rather than novelty. It was an attempt to take questionable novelties out of Lisp (like hygienic macros) and to clean up ill-thought-out interfaces (the keyword choices you alluded to).
"Hundred Year Language" is a bit of misnomer. Graham's original essay is a thought experiment on what the language we will be using in a hundred years will look like. Graham believed it would be useful to try and implement the language we will be using in a hundred years and in doing so, came up with Arc.
I've reread the article and You are right, the author's intention seems to be getting rid of unnecessary constructs. I guess then that I'm looking for something that Arc is not (powerful abstractions included in the language from the get-go).