a 2nd layer for doors makes sense since you always know what ground is beneath it, i get that. But isn't it an item already in that case? just with their own layer?
A weak, technical idea to justify the split:
Dungeon "Features" like doors use to have very simple states, and usually only one usage. Items are more complex in most games.
If you have items that can block movement depending on their state, they might serve as doors. It's not really a strict yes or no decision, but I'd keep items and features split.
Further rambling train of thoughts:
One can image a ladder of complexity, roughly like this:
- Ground/Decoration: Stateless and passive entity.
- Feature: Stateful, very simple and passive entity
- Item: Stateful, complex and passive entity.
- Monster/NPC: Stateful, complex and active entity.
Depending on your game, you can merge them into less categories, or also split them up further. I assume it's mostly a question what makes sense to you. Categorizations that you feel to be sensible allow you to work swiftly with them. So I'd not put technical arguments first here, but they way you think and handle your game development.
