I know Tom is generally against too many multiple tees, but it sounds like a problem that could be solved by them.......
For most courses, a 400 yard par 4 from the tips would also be only 370-80 from the middle tees, and 340-360 from the "whites" which is still reachable for average players.
I do know what he is saying, though. I struggle with designing greens for holes that distance, because even with middle tees, the old guys are reaching the green with a fw metal at 380, and need a big green. The top players have a short iron from 400.
A small green is too hard for the average guy, a large green is too easy for the good player, and a mid size green just doesn't seem to fit well for anyone.
I often use a big, "greens within a green" multilevel green at that length, but even that is a bit unfair to the shorter hitters, since they are likely to be far from the hole and unduly punished with a three put op after a nice shot.
Perhaps the best option is a large, well to overly contoured green? Those slopes might spin a short iron shot away from the hole, or make that shot difficult to control for top players. Also, I think the wild contours would probably bother the average guys less than the top players, since they are used to those longer putts. At the very least, it would probably make the chance of the good player one putting for birdie less than the average player three putting for bogey to kind of equalize things?
Just a thought.