I think one should ask the question in a different way, should most of the other subspecialties be integrated ones? Where I'm we are looking over the whole surgical residency. Cardiothoracic and plastic surgery had been on their own for decades. Now (since 2015-16), they are joined by vascular, peds, and urology. There are plans to do early sub-specialization, 2-3 yrs common trunk and then of to the subspecialty of ones choice. Why should future endo and breast surgeons do years of laparoskopik surgeries? extremely few will go into endocrine surgery involving abdominal cavity, and that will soon be centralized so future adrenal/pancreatic surgeon will have their second part of residency tailored to their future career.
Then we have the so called trauma surgeons, even in US they are not calling them selves that anymore, they are acute care surgeons! So their residency will be tailored as it is today and no way to do it differently! We are expected to get in all cavities, fix the problem (at least damage control), not do more damage, and get out… Unfortunately, most residencies are not good enough to produce trauma/acute care surgeons (both in US and Europe), but all general surgeons call them selves trauma surgeons!
We have already started this process at my hospital, waiting for national directives. I do take all acute cases and consults coming in and cover all the services during the night, except esophagus and pancreas service (their complications are out of my scope, and probably all future acute care surgeons too due the centralization of theses surgeries).
So, the general surgery residency as it is today will produce future junior acute surgeons, and all the other sub-specialities will be integrated ones (in my country).