It's likely that the fairways will be bentgrass, and the mown rough will be kentucky bluegrass, along with fescue bunker faces. No, you can't just buzz bluegrass down to a bentgrass fairway height without it looking nasty. And you can't grow bent up to rough height without it being a terrible mess. So those fairway/rough parameters will be in place unless the club uses sod to replace fairway with rough for the US Open or something. At that level of a property, whether it's OHCC or WF everything is on a separate irrigation program. So you would have heads covering the fairway throwing in along the perimeter, and heads along the rough perimeter throwing out. So arbitrarily moving fairways around and shrinking/expanding would create irrigation headaches.
Grass types like fescue or bluegrass can be maintained both at fairway and rough height, but fescue struggles with cart traffic, and fairway bluegrass has to be maintained at a higher height of cut and is less aesthetic than bentgrass (although it can be a fine fairway surface).
I think DeChambeau has made landing strip fairways and nasty rough irrelevant, so hopefully OHCC is getting reasonable fairway widths and they'll be left alone.
But I wouldn't bet on it.