Something that has already gone through two iterations, is what I am making sure I do my best to keep consistent. Which is the ability to talk to (at least, abstractly) every single person that you encounter in the game. They may not all have full on conversations. They may not all have rumors to tell, or plot points to spill. Some might even have things to sell strangers, or just friends. But everything with a personality, will (should) be able to be interacted with at some level. All the way up to murder, and possibly theft. (Though that part may come at a much later time)
With some creative use of a few of Hime Works Plugins, (for dialogs/shops) part of some plots will require the active investigation of the player in order to progress. Such as, gathering rumors or asking opinions. Possibly even earning trust (faction) with groups or individuals in order to gain access to information.
One thing I may have forgotten to mention… The entire demo will be released un-deployed. So anyone will be able to see how each part was done and use as an example for their own work.