One of my current long-term projects involves working through the planets (classical and otherwise) using a similar approach 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 neopaganism, eastern traditions, and the chaos magic metaparadigm. 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 fixed stars. Although a third book is a definite possibility, it is far off in the future and nothing has been set in stone yet.