Recognizable, simple, unique, and scalable. Sure, it works as a logo.
I didn't see the arch and letter motif until it was explained. I think this was the case for most people. It's much less than subtle.
In my mind, an arc/arch is all about the curve; it's the fundamental and universal shape of timeless strength. (I'm guessing that's where the name originated.) Because of that, I'm having a really hard time connecting a square, blocky image to that idea. Orthogonality != Arch.
Icons need contrast and primary colors are a fair choice. But I'd tweak them a bit. At first glance, I was reminded of the default MS Paint palette or an maybe 8-bit Sol Lewitt. I think I'll help with the blue/black scaling issue too.
Arc isn't finished, and I'd guess neither is its logo. LISP (and its dialects) historically have had very atypical logos, so it's refreshing to see something new and thought-out.
