There will be a time in the near future that you will not need to AI upscale textures manually. The engine will do it for you while playing. Currently, the process is too heavy and slow for this to happen, but give some some years and it will become common.
When you say "Any 'upscaling' is inevitably going to take artistic effort and the same skills as it did to originally create the asset. " i suppose you are talking about human effort? It this is the case, my opinion is that to make a statement like that, you first have to understand what art is and if it can be replicated by computers. The answer is yes, of course. We already know this. Specially because "art" is such a subjective thing.