If templates isn't feature rich enough, I imagine it is just a matter of time before someone implements a more complete OO system in arc.
In the meantime there are a bunch of schemes and lisps that support different object systems. You'll want to look for CLOS (Common Lisp Object System) and MOP (metaobject protocol) in the descriptions. I've used gauche scheme and had some good luck. http://practical-scheme.net/gauche/
