One more possibility, based on the assumption that they're taking the alchemical symbolism seriously rather than simply because it sounded cool...
Consider:
We have Plumbum (lead), Argentum (silver) and Simulacrum (the false paradise? Fool's Gold?).
The goal of alchemy was to turn lead into gold by means of the Philisopher's Stone (a.k.a the Philosophic Mercury).
The title Sibylla Aurea (priestess of gold) is likely something of a hint.
Perhaps the result of Neviril and Aaeru's journey will be to somehow turn Plumbum into Aurum (a golden age?).
Would this make either Aer (air) or Aaeru (love) the Philosopher's Stone? The latter would be quite fitting, in a way.
Of course, this still leaves an uncomfortable number of things (Argentum; Tempus Spatium) in need of a place in the theory. Anyone more versed in alchemy than I is welcome to chip in here...
Pah. We'll probably just get shiny things going boom.
