I took a quick run at Astral Form on my Ancient One datafile conversion. I'm sure there is more that could be done with it, but that served my purposes in the first draft.
viewtopic.php?f=15&t=274#p2653One thing I wanted out of my astral form was that the character was limited to the astral form power set when in that form. Most uses of astral form that I've seen in comics/movies/RPGs has the character mostly impotent when it comes to affecting the phyisical world while in astral form.
So using the Ancient One's Astral Form power set shutsdown his other power set and vice-versa.