For now it's just a brain dump! If there is anything stupid written below, that's why :)

Intent

It should allow users to trace over 3D models. Examples:

• rooms
• buildings
• posed dolls

Needed functionality

• easy to manipulate 3d objects
• easy to pose a doll (either in Blender, or in Krita)
• easy to trace them in Krita
• seamless experience

Implementation

Option 1: 3D in Krita

Option A

Option B

Option 2: Integration with Blender

"Blender file layer"

• there should be a way to just show the view from the camera instead of current view (maybe two options, current view as default for ease to use?)
• I guess there might be Python API that does that?
• maybe a Python plugin to install in Blender, to get it nicely?
• it could just render the camera view with Eevee (faster! we need fast - but it could be configurable, maybe? maybe just current render configuration, or, some default for basic users, and configurable (in Blender, not in the plugin!) for advanced users) to a file, and Krita uses a File Layer for that specific file (with a special name in a special place) - when closing Krita, it should remember the pixels so it can be opened without needing that file, possibly? (why our file layers are not like that? it really could cache the content...)
• the Python plugin could have some "new to Blender" basic options (necessary for stuff you'd want to use it in this context), like "move to Pose mode" for posing the doll.
• the Python plugin could have posable 3D doll (we'd need someone to make it!!! for CC-BY or even CC-0 - could cost money or we could ask on Blender Artists forum, someone could do that for free for us. We could find an existing one but I'm not sure if there really is anything there. I've seen, it's either cartoony, or without a skeleton, or it's anime - we should either have an array of options, or just one androgynous human-like doll).

• note that this might be a bit too inefficient, with a file as a proxy.
• think about different ways to move data from one program to another?

Blender just render the reference image every now and then

• there should be a way to just show the view from the camera instead of current view (maybe two options, current view as default for ease to use?)