Having done maps for a long time, I realized that one of the major limitations to EO was a lack of an expansion beyond the XY grid. While obviously in an isometric 2d game, it can provide 3d-esque views such as via shadows, shading, and whatnot.
Anyways, there already exists a way to somewhat break the 3rd axis that is already in the EO client. If you are ever blocked from view by a wall or object your character sprite still shows up. A similar mechanic could thus allow for tiles and objects to be "grayed" out underneath.
Obviously this would also present other features needed to be added such as an actual functioning Z access and updated grid/minimap system, and things like new sprites for walking at slants, etc.
So, for example, on the image below the center tile would be either 2,2,0 ; 2,2,1 ; or 2,2,2 depending on elevation. Just a rough concept, but I have yet to see it implemented in any Isometric game.
---
Former multi-server mapper.