Onions really hate competition so I think you would end up with just potatoes and some very weedy looking onions, I have never heard of onions stunting potatoes and I certainly have no problems growing potatoes where onions were the year before, I have never tried to mix them up as potatoes are such large plants and need space for hilling/mulching.
This year I planted carrots, onions and radishes together. So far its working great. add a bit of sand to thin them out. As the radishes have come on , I pull them, and it makes space for the others. Due to my space limitations, its been a win so far.
If they did grow together, i dont see how it could be done succcessfully as potatoes need constant hilling of dirt.
If you send it by car it's a shipment, but if by ship it's cargo. This tiny ad told me: