We want to remove the native material editor, simplify it all and put it in the inspector.

No, please don't move Material Editor to the inspector like in Unity😭. 
I hate the Unity Material Editor. It's just so horribly designed, and I don't think it can be improved.

Yes, please make a material editor in the inspector. If you also give the opportunity to take textures directly from cloud materials and make your own materials with these textures, it will be a breakthrough. I constantly see a lot of cool materials in the cloud, but they always have nuances that I wanted to change but I can't because they are compiled

Please, current material editor is insanely laggy on my end, takes for ever to compile, has several issues, etc

as long as it isn't a poonity clone

Honestly, it was hard to figure out how to load materials into SBox the first time.
I'm completely new to working with engines and only know theory and have some experience creating guided games in Unity.
I'll describe the problems I encountered when loading the model and materials into SBox.

1. When creating a material, you can't add maps until you save the material. So, I spent 5-10 minutes like a fool trying to drag-drop textures. Then, through trial and error, I figured out that you first need to save the material before you can work with it.

2. I was really confused by the fact that I couldn't initially insert a metallic map into the material. My model's textures were in the PBR metallic Roughness pipeline. I loaded all the maps except the metallic one and started randomly clicking buttons, hoping to unlock the metallic slot. Imagine my surprise when I clicked the Glossiness button and unlocked the metallic one. As I understand it, the button is needed to switch from PBR metallic roughness to PBR specular glossiness. But in specular glossiness, specular is used instead of metallic, and the roughness map needs to be inverted to get glossiness instead of roughness. Basically, I still don't understand why things are set up this way.

3. Normals. Sometimes the normal map is combined with the height map.
Initially, there was no slot for a height map, but I found a button that adds a "detail mask" and a slot for a normal map.
The problem is that I now have two normal maps in the material.
I don't know if this affects anything, and if there's a preference for which map the normals go in, but it's very confusing.

4. IT'S SO HARD TO FIND OUT HOW TO APPLY TWO UVs TO ONE OBJECT. Honestly? It's quite convenient. You go to the Model Viewer and add a MaterialGroup. BUT, BUT. I spent 20 minutes trying to figure out how to set up materials on my own. I FINALLY GAVE UP AND GOOGLED, AND IMAGINE MY SURPRISE WHEN I NEEDED TO FIND A TINY, LITTLE, MAGNIFYING GLASS.
Dragon Drop doesn't work. I thought, maybe I'm missing something, so I went into the inspector and tried to add UVs, but you can't add two UVs to one object unless you've already assigned a material to that object in the model viewer.

I hope this is helpful :)