Chris,
The question of designing for all levels of players is a good one. There has always been the presumption that this was the case, but I believe as time goes on, that theory will change, because its harder to do so.
One case in point is that with active senior communities becoming popular, these courses could easily omit the 7000 yard tees as a waste on the target audience, recognizing that on a day like Father's Day, perhaps a few younger whipper snappers might have to play a bit shorter than they truly want when visiting dear old Dad. Is that extra real estate worth it for a few days a year? Depends (oooh, bad senior joke there.....) on how much the course thinks the tee sheets will be filled with outside play.
Ditto with many municipal courses, where the goal might be to increase junior participation, etc. Just as restaurants have moved mostly from general menus to attract all tastes to specialty Mexican, Italian, etc., I believe golf courses will tend to do the same.
The pro game still provides resistance, and Merion will add to that. No reason other than history not to have about 50-75 TPC tournament venues at 7500 yards, with tent space, infrastructure, etc. and let most of the rest tip out at 7250 max, with even more courses tipped out at the 6800 yards that the lower 99% would be comfortable playing, and maybe up to half the courses tipping out at 6300 yards that 55% of golfers prefer to play.
As to rough, that can always be grown one week a year. Bunker placement can consider defending par, but for most courses, it should consider speed of play (good by, front right green side bunkers!), looks (trying to preserve the tradition of golf with attractive, but rarely used bunkers) etc.
Boring to the purist? Sure. Targeted to the masses? Sure, but also giving the customer what they want, no?