Of course, longer grass means flaws in the sward will show up more in terms of playability. I don't know the height of typical links fairways, but I would guess something like 9-12mm. I wouldn't have a problem raising that to 15-18mm (if there were shorter areas around greens the same height as the fairway) and just push that height out 60 yards then have basically "natural" zones with a view to making alterations where reasonable. I don't think the subleties of design would get lost in grass that height. I think that is probably much better than 30 yards of 10mm then hope the 30 first rough is kept to something like 25mm. In my experience, once the idea of 50+mm is introduced as the rough then things can go to shit quickly. I don't see much of a reason for that height of grass except on "special" holes where 60 yards of fairway isn't enough.
Ciao