Really, I think what would be more ideal, would be to make this spec only available as part of a variant rule with "Knight Play". I imagine it as such: If you allow the use of Knight Level Play, a player after character creation gets the 150 xp, access to this "Force Sensitive Apprentice" specialization for free, and access to the Mentor benefit (the reduction in base force training).
...in which case they could leave it out of the F&D book, but include it in any era or regional sourcebooks. So it would be available in a classic Old Republic (up to the end of TCW) setting. Then if they do a witches book there could be a new spec in there.
I'm not sure they'll do a witches book specifically, but I would bet money they'll do a supplement covering most of the non-Jedi/Sith force traditions unless their license somehow evaporates before they get to it.