Last preview I said I was going to start doing textures, but after researching texture art for a while I realized I probably should handle the futa version of the model first since it'll need to be textured too.
The futa version is simply an extra model that attaches to the groin, and I sculpted it with some of the strategies I learned while researching texture art—preserve most of the detail in a high-poly sculpt, that detail doesn't necessarily need to be translated in the low-poly retopology, and then the fine details from the high-poly sculpt can be applied as textures in the low-poly version.
If I were more experienced with modelling, I would probably know how to implement foreskin as an actual stretchable fold on the model, but for now I'll probably model it as a separate attachable mesh. Similarly, I think it's possible to implement shape keys and jiggle bones to handle the flaccid/erect physics as well as customizable size options for the shaft/balls, but I'll know for certain when I get to that point.