Gopher,
Druid is a form factor iconic for Zu and you could view it as Zu's most "architectural market" product. Until we hear both Soul Supreme and Druid V, we won't know the relative results but I expect Druid V to have more sophisticated cabinet composition than Soul, so the drivers composition may not explain all of it. Druid V's machined aluminum plinth should also have some sonic benefits over Soul's plinthless bottom. But even if one performs as well as the other, there will be buyers who choose Druid on form factor alone. I expect Druid V to sound a little better than Soul Supreme or at least tilted to a somewhat different bias, as Soul Superfly is a more forward sounding, striving and punchy speaker than the more relaxed and bohemian Druid 4-08 that inspired it.
Phil