I could do that, however, think of all the things you'd need to clarify in order to make it work with the current rules:
- If you're reshaping the board to 3D, what would happen to the squares we have now and all the stuff on them?
- How would "less than" and "greater than" be handled for square numbers (for items such as the Jetpack)?
- What would "sequential" mean?
- How would "passing over a square" be triggered?
- How would a player's "direction of travel" be determined?
- How would laps work?
- How would trees appear?
- Can squares still be destroyed?
- etc.
A proposal that would actually make the 3D system fit into the game now would either destroy a lot of the stuff we have now, or would be 20 pages long. All this being said, maybe the 3D system would best be saved as an early proposal in Nomopoly VI.