Yes, it is possible to do for all forums. It`s an administration option.
However, since RSS exports do not use a permission-based system, I would only do that for public forums. No members-only topics will ever be available in RSS format.
As such, would it be useful? Should they be exported separately (i.e. a separate feed for General Discussion, Real Estate Discussion, etc)? Or should there just be one feed that exports all public forum topics in one?
I appreciate input. I`ll enable these feeds if there is significant demand.