It doesn’t make much sense.
Vertex paint uses vertex.
If you remove the vertex in a mesh (using nanite) then why would you use vertex paint?
I seriously doubt they’ll ever patch or adjust the engine to allow this - though I’d love being proved wrong in this case…
Realistically its impossible. They’d habe to generate some sort of runtime render target texture to persist on the item. Not impossible, but it ain’t cheap.
Meanwile…
Assuming you actually want details and such to work, you have to paint textures rather than rely on vertex paint.
You can do so in engine.
First look up render targets.
Second, look up the old tutorial on render targets and water displacement, which as outdated as they are they still teach you some decent basics.
Third, apply what you learned to create a system to paint onto the render-target in editor.
Once happy you probably want to save out the render target image you produce to use it within a non editor material that’s applied to the final object.
So … its a 300 step process between creating the editor only material, the system to paint on the object and the final material to use on the object in the actual release…
Not hard to do, costly to paint, but not necessarily to render out…
Better than but similar to how landscape layer paint works, in theory.
Also, you do have 4 channels to use on the render target, so you can paint up to 4 layers per item if you use utilize the channels as layer masks.
You can do the whole thing the same way outside the engine, which is likely your best bet.
The real problem with that is setting up your DCC to show you what the final product will look like as you paint the texture.
Its probably easier to build it all in engine to be honest.
Particularly when the engine tends to visually render whatever it wants rather than rendering out whatever your PBR materials tell it it should render 