Over the time reps have increasingly become better as the rep market grows in size. I don't see the quality and technology of rep makers decreasing, rather the opposite. But I also get that it's not worth it for the manufacturers to copy every little detail 1:1.
Imagine a hypothetical scenario, where all the most popular watches (Submariner, DJ, Royal Oak, 5711...) were repped to such an extend, were it would not be possible, to tell for certain through the watch alone it wasn't real. Of course the watch may still be authenticated through paperwork and the AD who sold it.
It's highly likely that the reps would still be cheaper (smaller profit margins, no R&D and advertisement costs, less management cost..). Do you think the broader watch market would just collapse on the demand side? Or do you think the value of genuine watches would be shifted more on the artificial side (similar to paintings).