Tom,
I surely don't know the course as well as you do nor am I pretending to. My basis is past U.S. Open venues and what has happened to them. Shinnecock Hills I view as an exception as it was well tested more recently before the 2004 Open. It is also a very different kind of golf course.
I would love to see Merion host the tournament and frankly I think it would hold up just fine as is. I'm just not convinced it would be left alone especially by 2015 or whenever a date in the future would open up.
I just wish they would take the approach that they do (or used to do) for the most part for the British Open. I remember asking a buddy of mine who is a member at Royal Birkdale what they do to prepare for the tournament. He said, "they toss around some extra grass seed, throw up some grandstands, open up the back tees, and let the boys have a go"!