Generally, the community is overall unhappy about the control layouts. Very few of them are liked at this point for most, including myself. It would be great for 343 to add button mapping, as it allows for everybody to play comfortably and nobody can argue against it. However, it is much too far into development for such a thing to be coded into the gae, and it would most likely have to take away from another part of the game.
However, it is entirely possible for button mapping to be added vial title update for the game. Valve has done it for portal 2. Portal 2 started our with 3-4 mediocre layouts, but a month or so after release an update was released, giving full button mapping to the console players of the game. This proves such a feat is possible.
It may take several months for 343 to code in full control customization, but the payoff would be more than worth it, and I for one am willing to struggle through a few months if it meant that the future held the key to comfortable controls once more. Since this is post release, they also would have plenty of time to code in and bug-proof these options.
This would do little to interfere with current projects. The only things they would be working on at the time is plot development for halo 5 and updates for halo 4. DLC will most likely be handled by certain affinity, as most of the spartan ops missions and multiplayer maps were made by them. I’m sure a small team of 3-5 programmers could code this into the game in a few days time, and another few days/weeks to fine-tune and de-bug it.
This task may be an undertaking, but this simple feature will aid the game immensely for many, especially those unlucky gamers who happen to be handicapped. 343 would be doing everyone a favor to add this in as an update to the game.