First I will start by saying this is a wonderful tool, and I very much appreciate that it exists! Thank you for all the love and passion you've put into this creation.
Your most recent post in this topic was helpful for me as a new Mannequin user, as I had the same question about applying customized settings across all expressions. That's very useful to know.
I was really surprised to see a robust selection of poses with a variety of options available to choose from. I thought that was quite helpful to have built into the program. My suggestion, or request if you can call it that, would simply be asking about the possibility of adding some non-standing pose options in the future? This is really more of a "food for thought" kind of thing than a request necessarily.
My only other experience with this sort of thing is using VRoid Studio briefly, and for that program, you are able to export created characters to VRM format. I know of two particular software applications that can then be used with an exported VRM character to pose them in a specific way.
One is called VRM Automatic Photographing (https://matsuvr.booth.pm/items/2223918) and if I'm not mistaken it collects and uses freely available preset poses from other sources? The other is called VRM Doll Play (https://booth.pm/ja/items/1654585) and allows you to custom create your own poses manually by hand for your characters.
You already have just as many, if not more, standing pose variety options available in Mannequin, which is great! I just can't help but wonder if having others like sitting, kneeling, laying down, etc. sorts of poses might make things even more dynamic and interesting. But, I know when you start getting into the more unusual poses, things like physics/gravity start making it more difficult for clothing, accessories, etc. to translate over in a uniform way too.
I'm not sure which would be more difficult on the development side, either implementing additional poses for sitting/laying down/etc. like you already have available, or adding a VRM export option like the existing one for Inochi2D Creator (I'm guessing VRM is more meant for 3D models, so wouldn't really convert easily?) I tried looking into using Inochi2D Creator, but the options were overwhelming, and the complexity level seems to be beyond my current understanding. I was unable to use it at even a basic level. Alternatively, perhaps there is some other existing software similar to VRM Doll Play but that works with Mannequin characters that I'm unaware of?
At any rate, thanks for your time in reading all this, and for all the wonderful features you've already made for everyone!