About MMD (.pmx) support
A few hours ago, users asked to add MMD support (.pmx).
However, having studied this topic enough, I have to admit that I cannot add support for the following reasons:
Converters can not be used for commercial purposes without the consent of all authors.
The distribution of converter plug-ins, without the consent of all authors, is prohibited.
Moreover, the use of MMD models in applications is prohibited by license.
However, if you want to use the MMD (.pmx) model for personal use, you can download it using Unity. To download to Unity, you can use plugins found on the Internet (for example, MMD4Mecanim). Also, on the Internet enough video lessons on this topic.
Disclaimer: elfinikgames not related to MMD4Mecanim, MMD
Workshop (.pmx=>Unity=>UDCE=>Workshop):
If you upload a model to a workshop and it will not violate US law, Steam rules, or copyright, there will be no complaints about it, most likely, it will not be deleted.