Had another idea.
What if, instead of immigration, you could get new population by capturing hostile ambusher or sieging forces, and then transforming them into succubae? Using a soul wisp, maybe, at a summoning workshop. I know that siegers have their own profession and skills, put I have no idea if this idea can be done. The genders can be assigned in the current percentage too, so you'd have many more females than males, and thus this kind of population expansion would be the main way to advance, rather than breeding and immigration as with dwarves.
(Of course, this is a tame mod, so "poof, you're now a succubus, enjoy your new boobs." magic works fine, but if you wanted to make it more in-line to its spiritual predecessors, you could require that the transformation take place in a room with a bed and chains, while the transforming succubus uses a whip as a weapon. Potentially taking less time/ be more efficient by it having high points in social skills like Persuader/Negotiator. Sort of 'selling their soul', kind of deal, if you wish.)
I know that something like this is planned for the patch after the next one, but I think that the twist I gave it is way more interesting to someone who wants to play the game differently.
Also, I am not sure whether this happens or not, but maybe make the lust demons not require alcohol at all, and be abe to live and work on water only.