Mike Do and I have been doing a narrative campaign for a few months now (5 games to be exact, 1 of which was a Planet Strike mission), and it's been moving along pretty well. We've come up with an "XP" system where units can become stronger or gain a Special Rule when they acquire enough XP. It's still in a development stage, but we've been fine tuning it as we've been playing. If anyone is interested in what we've come up with, let us know and one of us can forward you what we have.