The Swarm opens up doors as far as doing high-efficiency speakers, something I thought would be the case but then one of my customers paired up a Swarm with his Edgarhorns (the Titan sub being impractical for his room), and when Swarm was dialed in it sounded like his 80 Hz front-loaded bass horns went all the way down.
Once we've crossed the threshold and decided to use the Swarm, all of a sudden there's really no reason to pursue bass extension south of 80 Hz or so because the Swarm can do it so much better than our mains. And all of a sudden the very high efficiency called for by single-ended triodes becomes a lot more practical to attain.
I have two SET-friendly projects in the works. One involves a high-output two-way satellite speaker, and the other involves a rather exotic single fullrange driver. Both are intended to be used with the Swarm.