As long as SA is as easy as it is there will still be players in tiers they don't belong in. It looks to me like a large number of new masters got there because of SA. Bringing the back nine isn't going to make it any harder because a lot of the greens are shared there and you will only be going in a different direction. It's still flat. Oakmont, however, should make it clear who belongs where if it's anything like it's supposed to be so I would much prefer Oakmont to the back 9 of SA.
I would hope that new tiers wouldn't enter the equation until all aspects of the real game are implemented, specifically lie factoring. I would be willing to bet that half the people carding low 60s now would skyrocket to the 70s, or high 60s at least, when they have to know what to do with a sidehill, uphill or downhill lie. The real golfers will get it fairly quickly while the gamers will be screaming deviation. Then we can see who knows how to golf.
In the interim, ideas like RGs for anybody that hasn't cashed or earnings based seeding in tier specific tourneys would allow a little more diversity until the Elite tier shows up (IMO you have to be dead to be a legend.)