There still seems to be interest in the project. The forum gets new topics posted every few days  and Anarki, a community ran fork of Arc, shows recent commits .
They were converting from Arc to Racket, but I don't know how much ended up being done (https://github.com/hubski/hubski/wiki/Converting-Arc-functio...).
And the main reason reddit was rewritten was library support. Doing simple things in CL was hard because you had to write it from scratch, but doing those things in Python was a simple library install.