Thanks. It's not the language itself that I'm concerned about. Rather, I'm wondering how much interest there will ever be in developing a truly fast Arc.
Consider Python, for example. It's been around for a while and is widely used. Yet it's still pretty slow. Fast enough for building websites, sure, but it's nothing like C or Fortran for serious numerical work.
Python's supporters will tell you that its slowness doesn't matter, because you can re-write the time-consuming bits of your code in C. I can imagine that that works well for web programming where latency accounts for much of the execution time anyway and one might only occasionally have a really chunky calculation to do. But in my experience doing Monte Carlo simulations, solving large systems of non-linear equations and that type of thing, a large part of the code is fairly critical for execution speed, so re-writing in C would mean doing a large part of the project in C. If I wanted to do that, I'd just write in C to begin with.
I've experimented with Ruby and Python lately, with the hard-care numerics to be written in C, as I alluded to above. I've not actually done huge amounts of programming recently, although in the past I did so in a proprietary language resembling C and in Fortran. Recently I have a look at CL (which accounts for my interest in Arc) and at OCaml, though I've not yet used either extensively.
