Toilets are the most tricky adaptation to tiny house lifestyle because the building inspectors are governed by the environmental health codes and in many places cannot approve alternates to conventional toilets. This leads to issues regarding expensive utility connections etc. Composting and incinerating toilets are only approved in a few places. Be careful here. Going back to my mantra of “convertibility”, you want to have the space and piping for a conventional toilet so you can change it out if you are forced to go legal. I have heard of places where they will allow composting if a conventional toilet is “available”.
Human waste is smelly and if untreated in a robust and legal way, can cause disease illness for TH owners and communities. Septic and sanitation issues will get you shut down faster than any other issues in terms of “alternate” systems. Do your research and design very conservatively. You don’t want a smelly toilet in a small, confined space.