Here are some personal notes and opinions:
-- I like the idea of Schala in some indistinct Zealian throne room as Lady Marle suggested. Zeal fits the aesthetic of the High Priestess beautifully. If you go with this idea and want to incorporate the traditional symbolism, there would have to be a fair amount of emphasis on Zealian architecture.
-- I personally think the pomegranates & veil would fit very well. Schala is very much a Persephone-esque figure, and it would be a beautiful touch. They could be highly subtly incorporated, opposed to how they are depicted on the card. If not this, then something to suggest her relationship to Lavos might be appropriate.
- The two pillars could be replaced with the Zeal statues, as has been suggested, and it would not be too much trouble to inscribe a B and J into them.
- Linking it up with the Empress - Queen Leene really isn't necessary -- there's already a physical resemblance between Leene, Marle, and Schala, which works beautifully in terms of the cards.
- The horned diadem, or crescent moon, should also be easy enough to integrate, and I think it would be fairly important. Alternately, some people draw a mirror, which has similar symbolism.
- There are established relationships between this card ad the Magician (undecided as of now), as well as the Hierophant (also undecided). If we can, it may be cool to link up the cards, but I realize that's a lot to ask.
Whatever you do, there's no need to strictly follow the Rider-Waite symbolism. The card has been interpreted in plenty of ways: the point is to get the general meaning across (and in this case, Schala is such a good fit that no one needs fret too much about tying tarot & Chrono together!).
Here are
a few different versions of the High Priestess card to contrast with Rider-Waite.
I'll post up some other depictions when I get a photobucket set up so I don't hotlink like a jerk.