I don't know. As I age, 12 holes seems about perfect now, as I tire a bit and lose what little swing I have playing through to 18. Maybe in a few more years, I will prefer 9, then 6, then 3, as I have seen with other senior golfers. They play as many as they can, go home, nap, drink beer or whiskey, have some dinner, go to bed. Rinse, lather, repeat the next day!
Or maybe, its just building 18 hole courses that return a few times. I Know when I worked at Killian and Nugent on the grounds of Kemper Lakes, we got used to playing after work, until dark and the actual amount of holes never mattered, and we played match play (which I liked). I also recall some guy in southern Illinois calling us, only to go down and find he had a 12 hole course. Our first reaction was "you can't do that" and he said, hell yes, its my course and I can do what I want.
So, maybe the 12 hole number is just sort of ingrained in me. I have no real method to back up my thoughts that it might prove popular in the years ahead.