You think right.
Now, first and foremost: this isn't even a beta, it's an alpha.
By that I mean that many things still don't work. This is for you guys to *play with* and let me know what you think, not to actually start making themes yet.
In fact, the only thing 'working' there are the panels for Nexus skinning. All the panels for other objects (Shelf, Menus, modules, etc...) will be blank. However you will find that most of the stuff in the Nexus skinning panels is already working, so it should give you a feel for how the rest will work too and how everything ties together.
If it's not intuitive, please let me know.
In theory you can already use the Theme Builder to make Nexus themes. You can also use it to automatically convert non-native Winstep dock themes to the Winstep format (provided those 3rd party themes are already available to Nexus).
When you run the Builder, turn on your speakers (but first make sure nobody is sound asleep on your household lol) - it's a little homage I made to those old 90's machine code PC demos, if you remember those.
Anyway, I'll shut up now and go make a setup program. Be back in a little while.