I'm gonna give a quick reply because I'm about to call it a night :)
The thing with the lipstick is that it can't just go with fixed pre-agreed spots - the engine does not know what a kiss is, and is completely agnostic to the actions / animations it plays. To have fixed lip marks means that the engine suddenly needs to know this stuff, and creates weird dependencies. It's not a good pattern. Yes, it works, but prepare for trouble in the long run.
One thing that I should probably throw in because it sheds some light on my approach to game development: I'm basically a one person team - I code, I do 3d modelling (which I'm still learning and not that great at), I make animations, I do game design, I do support and bugfixes, I do a bit of marketing when I can, I answer questions, do a bit of community management. It tends to make for a busy life :) What this means is that I have limited resources (time, mental capacity) and so I need to pick my battles, and also be extremely mindful of what could make my life as a game developer a lot harder. Antipatterns and added complexity and the 'and the kitchen sink' can be my worst enemy. So I try to stick to best practices as much as I can.
Clothing and wearables in general are probably my biggest nemesis when it comes to the game. Adding things isn't quite trivial, due to all the shapes that character customization allows. Clipping is a big issue, and it's horrible to solve, especially when it happens with shape (morph) combinations. You repair something and then it breaks something else. So while I am trying to add as many wearables as I can, it's not so fast going. Add to this the other things I'm working on, and it will be pretty obvious why so many things aren't (at least yet) in the game. I have a long list of ideas, suggestions and requests that is literally hundreds of entries long (not limited to just wearables, ofc). I agree, a lot of things would be cool to have, but when it comes to clothing, I think I need to first cover the basics. I'm now trying to slowly add non-revealing wearables, for example. More things will come in time, for sure.
Re: opacity - some things can't be made transparent, due to the fact that they hide the body part underneath in order to avoid clipping, especially when deformations go differently between the body and the wearables due to differenr distances from the bones to the meshes. In some other cases morphs are applied that instead of hiding the mesh underneath the wearable, they make it smaller. So while for some stuff the transparency thing may work, for others it would not.
Capes and mantles would need cloth physics and collisions to look good, otherwise they'd end up looking pretty wooden. I gotta say I haven't looked into it, but I would imagine it is resource intensive. Performance is something I need to also be mindful of, due to the game needing to run ok on mobiles too. However, ofc, things can be optional. I'd say atm capes and mantles aren't a priority. Would love to have them, ofc, but they'd need to function well enough and look good. Maybe one day.
Vampire and orc teeth are actually available as mouth/teeth shapes starting with v1.22 I think (or around that version). Their length is customizable, which makes things nore customizable than if using a wearable.
Freckles and body paint - maybe when I'm done with the stuff I'm working on now, or maybe a bit here and a bit there. I have put them down on the list, in any case.
Oh, another thing. While I try to take into account feedback and suggestions, I also make no promises and make a special point of setting expectations and letting people know I do not know and cannot begin to guess when I'd be working on / delivering something. Or even if. It's a necessity when you get a lot of suggestions and you know it takes time. Also, I do tend to work on what I feel I want to work in the moment, because it keeps me motivated and interested. There is no grand plan in the order of things, apart from some intentions, a long list of things, and the occasional random ideas :)