One possible idea which would literally use regiones as worlds would be to adapt an idea from MtA and have each realm present a version of each astrological planet; for example the faerie version of Mars might be populated with battling mythic heroes, while the divine and infernal ones might represent (very different!) versions of the field of Armageddon, and the magical one might be an abode of dragons.
In some cases, one or more realms might be squeezed out by others; a possible explanation for the Limit of the Lunar Sphere in Hermetic Theory might be that for some reason there is no actual magical representation of the Moon (it was long believed to be unreachable, this assumption was incorporated into Hermetic Theory, consciously or otherwise, and so it is rendered unattainable by the same weight of belief that makes magic possible; neither Hermetic magic nor mundane craft can reach or affect it?) while the Divine one is small and sparse of feature (not a large element of the divine plan?), the Infernal one is devoted to madness (lunacy and lycanthropy) and the faerie one is large and oriented towards mysteries, tides, and other enigmatic natural forces.
Such realms might be level 10 regiones themselves, or merely reached from certain regiones with appropriate themes (or resonances). To further develop the 3e idea of Arcadia being at level 10 in a faerie regio, there is no reason that the representation of Arcadia would be the same in each case; there might be many different aspects of that concept, accessible by different means from different starting points, conceptual or physical, yet each of which might seem like ’the’ Arcadia to its occupants.
Might the ‘science’ of Astrology provide a key to navigation to and between such realm-epitomising regiones?
I hasten to add that I haven’t consumed the sourcebooks in full, and the potential implications of applying such a cosmology to AM5 may be huge, hideous, contrary to canon, or all three.
As a fellow Mage fan, I approve of @Carologus idea. One could also steal ideas from Exalted where a Regione is a powerful being, i.e. where Malfeas, King of the Primordials was ripped inside out to create a prison for the other Primordials and losers of the Exalted war.
Have we mentioned Dungeon23 here?
An interesting possibility- Revelations indicates that God will "create a new heaven and a new earth" for the devout as part of the apocalypse, essentially abandoning the current earth (and the current heaven?) to the forces of evil. So finding a new world in a divine regione could be very troubling to say the least...
Which makes sense. At least 3 realms have canonical versions of the planets, the Divine has archangels as planets, the Faerie has Faerie god as planet, and the Magic Realm has the Astra Planeta.