Convert to Game Base - Some important issues

Full control over how materials are merged, when selecting Convert to Game Base -> Multi-material
Add an option so you can select which materials to merge together.

For example, you often want to keep the head on a separate material/texture, because its the most resolution dependent, and then merge all the other body/skin materials to a second material/texture.

GUI implementation:
Under [Multi-material] -> list the material in a table view, and in column #2 present a drop-down with all the material, its a simple interface for selecting material to merge, optional column #3 texture size. Example below.

[Ga_Skin_Head] [Ga_Skin_Head] [1024]
[Ga_Skin_Body] [Ga_Skin_Body] [1024]
[Ga_Skin_Arm] [Ga_Skin_Body] [1024]
[Ga_Skin_Leg] [Ga_Skin_Body] [1024]
...

You also want this feature in Export -> InstaLOD -> Remesher so you can control material merge/reduction per LOD.
Now all LOD are fully merged, that is not optimal, you want full control over this per LOD stage.