I would find a piece of rolling farmland and build my Oakmont. The name of the game would be penal, but rewarding in nature. Misses would be severely punished by deep intimidating bunkers. All bunkers would have to be boldly designed, even for the pros. The greens would have to possess undulations that require huge borrow for break. 10 footers with 4 feet of break is both entertaining to play on and to watch the pros play on. At least three greens that slope away from the player in some way would add to the variety. Is it a necessity? No, but I would want it to be included on my Open test. Not necessarily treeless, but to top it off, fescue blowing in the wind. Oakmont seems to have all these qualities.
Unlike Oakmont, I would want my course to be able to easily and strategically convert from wider fairways to the narrow runways the USGA seems to favor for an Open setup. I really want to be able to have my grandmother play the course and, at the same time, the low handicapper to feel challenged in non-Open years. Oakmont, specifically, would present grandma with some challenges in approaching 5, 6 and 13 because she couldn't putt the ball on from the fairway. It is my hope, with this design feature incorporated, that my course can exist being locally supported.
As to specific par requirements (par 5, 4 and 3 design features) , I feel the USGA does what they want. You can design a great par five at 510 yards, but if you can't stretch it (in most instances) it will become a par four for them. The par fives as a set (IMHO) should have two that are reachable and one three shotter. Pros are rarely confronted with true three-shot holes. I look forward to watching 16 at Olympic Club this year. I hate that the USGA tries to fit a driveable par four into most Opens. If it exists, or in the case of having a blank slate, if it belongs or can be fit into the design, then use it. In other words, when these conditions don't naturally exist, stop trying to add excitement to my course by using the forward tees. Long par fours (over 460) will, for the foreseeable future, always be on the menu in an Open. I'm ok with that and would design appropriate tournament tees to accommodate these conditions. My par threes, as envied on this site many times, would have as much variety as I could find. You can bring out the uniqueness of a par three by creating it to traverse a difficult piece of land, link two holes, and/or complement the design as a whole.
Boldness and/or uniqueness/quirkiness in whatever way you can find it should be demanded from those seeking to design a course for hosting an Open. My ultimate goal would be a course that makes both pros and laymen think and is entertaining and memorable to the average golf fan.