It's more of the former as I have a MASSIVE love for slime girls and as such it'd be an absolutely dream come true to have the MC be able to have a "slime girl" option. if not at the start of the character creation then hopefully later down the line in the story, though given the vast amount of racial choices at the character creation settings, I don't think that adding "slime girl" as an option is too far-fetched.
Addiction... got it!
Also Slime Girl body might be a No-Go! But he might add a Slime Girl NPC though!
(So for answering the Confusion on why no Slimy body, it requires a lot of work and as he mentioned he does plan to Add wings, More Horns, etc, but not Body altering traits like BeingFAT so yeah... I mean you can always wait for a responce I guess?)