Does anyone know?
No it has not been confirmed
You might find this interesting. Particularly:
> Players who were worried about the button layout in Halo 4 an ease their concern as the button layout in the game’s presentation at RTX was fully customizable. At the present, the game offers a variety of layouts to choose from including “Bumper Jumper”, “Green Thumb”, “Boxer”, “SouthPaw”, “Recon”, and “FishStick” in addition to the “Default” setting.
> Likewise, 343i says that the layouts aren’t final, and as such they’ll be listening to player input before they finalize it for the retail version of the game.
By the sounds of things, the build at RTX enabled fully customisable controller schemes. However, it then also hints at the fact that the final build will only contain set schemes.
I would take this with a pinch of salt; A lot can still be changed before the game is released and I think there is a good chance that they will enable fully customisable controller layouts. Or at least make the schemes more favourable with what the player’s want.
But to answer your question, at this present time, customisable controller schemes are not in.