Hey! Thanks for your (very well-worded) question! We were actually hoping someone would ask this.
You are 100% correct in your assumptions! If you have the skills to work with your engine of choice, then you are more than welcome to experiment with the SOUP-like format as long as its kept within the same general spirit and limitations, as you mentioned. The only reason we don't explicitly say this is allowed on the jam page directly is because we didn't want people to misunderstand and just submit regular walking sims to the jam. Anything submitted should still clearly be inspired by SOUP and follow similar minimalist creative restrictions.
For example, absinthe is inspired by SOUP while still doing its own thing, and MaximumWalk (while not being inspired by SOUP as far as I know) is a similar type of game that feels like it was molded from comparable thought processes.
All of your examples are excellent ideas and would be allowed. We experimented with the SOUP-like format ourselves with SOUP ROOMS by adding an "interact" screen layer that appears when you get close to the central object, changing the left-click pop-up image for each room, and a few other relatively minor things (like animated screen layers) while still keeping the general SOUP format the same.
Thanks for inquiring and for your interest in the SOUPJAM!