I believe you don’t get my intentions yet 
This kind of approach would allow the user to create the textures dynamically in code and to use them MAINLY with parametric meshes. With parametric meshes there is no remappping of UVs because you are defining the UVs when creating the meshes. So this is not about loading a textured mesh and create a texture atlas fromt its textures.
As an example just imagine you would like to create a visualization of user connections between BabylonJS forum users and you want to display the avatar + username + add a badge with number of connections + draw lines between these entities. You can create a texture atlas with all user avatars, draw the username and the badge using canvas2d on the texture and put all textures in one texture atlas. You can then create one parametric mesh which use one big texture to display all of this in one draw call.
Another example is the image wall: