I've found using import all the time to be a bit tedious. Could you consider allowing users to drag & drop images and substances from windows explorer to painter?
I'd like to see drag & drop in all possible places, for example you could just drag an background image to your pbr viewport and it would change it instantly.
To populate previously made texture maps, you'd just drag images in fill layers without having to import them separately before assigning. If image would have standard naming convention and have something like _normal, _roughness etc in filename, it could also change fill layer to act accordingly without user input.
To add multiple textures to the painter, you could just select them in explorer and drag them to texture section and so on.
I think having such feature would speed up the overall workflow in Substance Painter.