Dave Winer has proposed a roadmap for merging Atom and RSS 2.0. So far, negotiations have not collapsed into a flame war. I'm guardedly optimistic.
I'm not sure that the most ambitious goals for Atom can be reconciled with what RSS prizes most -- backward compatibility. But XML gives us a precedent. An XML document can be well-formed, which means that it adheres to a minimal set of rules, or it can be valid, which means it's well-formed and it adheres even more rules. Perhaps some middle-ground can be found along these lines.