In my opinion, this is quite feasible.  What will you need?  1 CG scene.  + additional line of quests.  + additional dialogues with NPCs, allowing you to invite to the cult (Persuasion Wisdom 20; Prostitution - high sexuality; Intimidation - impressive warrior).  just moving some NPCs to the temple... and an orgy in honor of the sea witch.  maybe some values in the status, here it’s easy to add an effect like Happiness/Womb with 10 levels.  Add Dialogues with Cultists.  Perhaps give the Sea Witch the Sacrifice perk, from the Cult, which allows you to sacrifice enemies in exchange for buffs?  If we take the Maximum program directly, then the opportunity to create Relics of the Sea Witch, and recruit new Priests and Priestesses, who can be met in cities/in refugee camps.  To summarize, in my opinion, you can do without a CG scene and do something quite interesting with minimal time spent on new coding.  This would be a very cool reveal of the Deep One race.  Perhaps the only real drawback would be the need to add content to other races.  But even here I see good options.  You can give additional abilities to the Abomination by absorbing the corresponding Abomination Boss.  You can give an additional social branch for the Crossbreed.  In my opinion, this will only make the game better.