Don’t tempt me. Part of me wants to do exactly what you suggest (just to see how that UOA would look).
Other than fear of being labeled a heretic, what's stopping you?
Don't do it all at once.
First, run out to 15k miles; do a UOA (it's very likely to come back as good as this one)
Then, perhaps try 18k miles ... UOA
Then 20k ... UOA
I would add that if you're going to push out the OCIs, you should consider a high-capacity, high-efficiency filter (perhaps Fram FE, or similar).
You see, you'll never know where the limit is until you test out further. It's not like the engine will implode if you got a slightly higher wear rate at some point. Don't let frantic people gode you into short OCIs.
Fuel dilution isn't an issue; these engines don't have DI. So unless a fuel injector just poops the bed, it's a moot topic.
Other contamination can be easily seen in the UOA. While BS does not give soot or oxidation values, they do have an "insolubles" count. As long as the insolubles count is .5 or less, it should be fine. I think there are better methods of testing, but the insolubles valuation is at least some measure of the combination of soot and oxidation byproducts.
The wear rates are very, very low. As long as contamination isn't a problem, there's absolutely no logical reason not to extend the OCIs. I'm confident the combo of the 2GR-FE and Amsoil SS are more than up to the task.