I believe you mean the Urxen and the Mancer races? They are still in the game files, and can be activated. When I got FE it was at a point in development when they were already oficially taken out. I'm not sure why. Maybe they dominated the other AI's too much during playtesting? Or maybe the other way around, and they were too weak? Maybe someone who has played long enough to remember that can answer this question.

Despite them being taken out I liked them enough to put them back in the game manually which isn't hard to do because both races have their sovereigns changed into heroes in the unit files, but these can be switched back being sovereigns. At least that is what I did. I'm not sure if I remember right, but I think they even still have their own intro narative and everything! I recommend that you take away their starting gear and tweak their stats to that of the other sovereigns at the game start for balance purposes. If you want I can just give you the files if you prefer that instead (assuming you want them in your game).

I love Umber as well.

Derek said they will not be restored in LH a few months ago.

I do not like this.  If anything, this game needs 12 factions.  (DLC factions is something that would be a good idea)