Thanks for the offer, Miru! Pulse0 is kinda right about BlitzSonic levels... but eventually people will be able to make their own levels for Project Nexus, so I won't even need the levels. Actually I hope to create a whole bunch of pre-constructed set pieces. Pipes, ramps, grind rails and such. Maybe piggy-backing off of an editor extension.
Pretty much all that's in the way of me getting a tech demo out is the camera system, some basic RPG functionality, and the water physics. I'll start analyzing some other camera systems when I get time, but what I am particularly interested in is how fluid drag works in Unleashed and/or Generations, as well as the precise logic behind the force slowing Sonic down while water-running. If you'd like to poke around and find out how drag and water-running work, that could help me complete the basic physics faster.
For the RPG functionality, I'm basically trying to think up a good way to handle actions. As I've mentioned, I want them to work in a system similar to what you might see in an MMO like WoW or something. That way creating larger, more complex button mapping will be easier, and adding new characters will be much easier. My current idea is to make actions ScriptableObjects Since they don't get any Updates, I might have them all just work on some kind of "Tick" event system built into the character. Then if they need any additional functionality in-world, they can simply spawn some GameObjects or something.