I'm not planning on making Bronze Age my life's work like Toady is with Dwarf Fortress. It's actually the longest I've stuck with a game so far, and I've made it through a couple burnouts. Focusing on the core gameplay is a guard against future burnouts, so that there will be a playable game no matter what.
My hope is that after the next few releases it will still be flexible enough to add new features, but won't feel incomplete without them.