After a while I changed my mind regarding upcoming album "alchemy" theme. I agree with
@TheMercenary in a sense that new album will be set more in sci-fi realm.
The Mandrake Project does not sound overly medieval, also we know about Necropolis from
If Eternity Should Fail. Album narrative may be seen more from aliens perspective. There is a theory that
pyramids (Roy Z mentioned those) were built because of aliens. Also promo picture indeed does look like some sort of ancient hangar/space ships landing place. So, some dark form of aliens will kill indigenous people to obtain eternal life (here's
mandrake for you). Album may sound Chemical Weddingish, but lyrically it will lean more towards dark sci-fi. Such is my prediction.