One of my current long-term projects involves working through the planets (classical and otherwise) in the same spirit as with the elements in The Elemental Magic Workbook. Overall, The Planetary Magic Workbook will be heavier on Judaica and ceremonial magic but will still address the planets in witchcraft, eastern traditions, and the chaos magic meta-paradigm. It will also explore potential magical applications of fictional planets (such as Arrakis from Dune, and Qo’noS from Star Trek).
Another long-term project involves investigating the magic of the zodiac and other fixed stars. Though a third book is a definite possibility, it is far off in the future and nothing has been set in stone yet.