GTA 5 was released mere months before the xbox one came out so of course the already had plans to port it. The new xbox is only speculated at this point so it is highly unlikely that microsoft has informed developers of the specs because that is how leaks happen. GTA 5 had to be ported to work on xbox one because its client side game. BDX has dedicated servers so it won't matter what version of the xbox console you have, as long as you have the same microsoft account you can log into your game. If you don't understand this i can try to dumb it down for you even further.
I actually answered the question in this thread in the first(unedited) post yet you chose to bring up a completely unrelated game from a different time period that adds nothing to the discussion. Do a little research on microsofts plan for future consoles and you will see how actually retarded this thread is. I'm kinda glad that you've been watching me though, much love to my fans.