Proof for certain features can not be provided as it is all ascertained by hacking game files. You can look in certain files, not just configuration files, and find a ton of clues to features that are currently hidden. If you find these clues, you can make best guess assumptions as to how R* will eventually include this code.
I would expect that all those nice things left over in the files are unfinished ideas, buggy code that could not be fixed in time, or functions that had to be taken out to get the game to run adequately.
There were similar clues in GTA IV of buildings or houses for example that looked like they were going to be enterable or functional later, but it never happened. I think everyone believes that a lot of great ideas in GTA IV were left on the cutting room floor in order to get the game out the door.
I think those elements were dropped, but left in the code as benign nonfunctional bits, rather than try to extract them and risk buggering the game database.