Neil, good question and I think it's one we all wrestle with, if not consciously then, subconsciously. I would be that most all GCA's would favor wide, but most all super's would favor the opposite. So it probably comes down to who the client is (how deep are the pockets) and what HIS priorities are. The problem with notions like "Sustainablity" is it is what everyone thinks the other guy should be doing. But when it comes to his backyard, well....
If history has taught us any lessons, I fear that just like many wide fairways were narrowed overtime on classic courses, the same will happen with those being built today. It may just have to be a more programmed act. Unlike older courses, one cannot simply change the mowing pattern to narrow a fairway. Today you have different grasses and complex irrigation to contend with. But eventually, the year-in, year-out cost will trump a one-time expense and if that is where the priorities lie...say goodbye.
One thing that has the architect at a disadvantage is that he is never around to defend the design. And if the bottom line is of a greater priority than the original design intent, he will lose everytime.
You also saw this with the elimination of sand bunkers in the Depression and War years.
One unforeseen problem with this thinking is that once the fairways are narrowed, and the roughs enlarged, many times the scale of the two gets out of whack and they just plant some trees to adjust the scale. So, not only are the fairways narrowed, but the effective playing width has been narrowed too!
Many times I have been charged with the task of making existing fairways play wider but not adding any more square feet of fairway turf. I call this, "Strip and Flip". But going in the other direction doesn't afford this possiblity and hence more expensive.
My guess you will see management companies leading the charge when it comes to narrowing fairways.