Yes, it will be a lot of work. At the moment the game uses one skeleton and one mesh (deformed and rezied) for animations involving characters of six different sizes. To cover all potential size combinations, one animation actually needs to be 36 different animations behind the scenes. To add a new skeleton, such as a lamia, you need to double it, to a total of 72 different animations for the same sex position. Let's say another skeleton is added, say a centaur. Congrats, the same sex position now requires 144 different animations to play. Want to add another? Congrats, now you're up to 288 animations.
This is the curse of breeder sims. This is why the developer has opted to reduce available content for the time. Every potential size combination, every body type combination, all of those need to be directly accounted for, by hand.
Lamias and other non-bipedal models, or additional potential sex positions. Pick one, because you're not getting both from a small-scale indie developer.
Edit: actually, my math was based on a flawed assumption that doubling the animation count would cover adding a new skeleton to the animation. This is only true if, to use the above example, lamias were only ever on one side of the animation. Seeing as this game is designed such that the breeding lets you pick who gives and who receives, every skeleton would actually quadruple the required animations. So adding lamias would take it from 36 to 144, adding centaurs after that would take it to 576, and adding another after that would take the required number of animations for the same position (to cover all potential combinations) all the way up to 2,304.
To use the game in its current state as an example, there are currently 79 different animations to account for in the existing sexual positions. (Compared to the 288 potential animations if all required slots were currently filled.) To properly add a lamia without noticeable issues with the animations or exempting them from a wide range of animations, another 237 animations need to be created. To add both lamias and centaurs (which were in the game's plans at one point or another, iirc), it would take 1,185 additional animations over what the game currently has. So please, tell me how that isn't actually a lot of work. I'd love to know your solution, because it's a solution that companies like EA, Activision, and Microsoft would pay a great deal of money for.