BodyTypeMatters

This mod will make the currently cosmetic-only bodyTypes (standard, thin, fat, hulk) in Rimworld have functional in-game effects, and always show up in the pawn's genes just like Hair Color and Skin Color by default.

This is accomplished by altering the bodyType genes (requiring Biotech) and converting them to germline endogenes through BT's Spawn Those Genes.
This also means that bodyTypes can be given relative frequencies for each xenotype (thanks to Spawn Those Genes), instead of each being equally common. (by default with this mod, the standard body will be much more common)
This method has some benefits, making it trivial for users to alter the stat effects of each bodyType, and their relative frenquencies for each xenotype, to personal taste with just some light XML editing.

Because of this implementation, custom xenotypes will require a patch as of now, but it is a relatively easy XML patch that should be trivial by looking at how this mod patches the base Biotech xenotypes.

I consider this unfinished, as I am still looking for potential issues, and I would like to make bodySize and healthScale effected, but this will require some C coding to make a new multiplier stat for them that can be effected via the genes. I am looking for some help with this, so please let me know if you have any experience and would allow me to pick your brain for a few moments.

Update: Added patch for xenotypes added by AlphaGenes (except Lapis, which does not have a bodytype compatible body). Since none of the xenotype have fixed bodytypes compared to baseliners, they share the same frequencies as them - easy to alter the frequencies in their xml file if desire.