I can't comment on the method you described, but I personally would take a tree I considered to be beautiful and let it grow (oaks are slow to begin with) on its own til it produced some acorns, and plant those, rather than taking a chance on compromising the 'mother' tree in any way.

Sounds to me like you'll end up with a graft-scar right where the nebari starts. This scar will never heal properly in a way that you wouldn't see it anymore. These scars will alway be a non-appealing eye-catcher.

If the part of the tree which you want to separate from the base-tree isn't esthetically necessary for a proper look of the base-tree itself, but you're certain it could make a nice tree of its own, than i would just try to air layer it and hope for the best.
Otherwise just chop them off, or try to air layer it anyway to see if you could gain some experience from it.

The idea of the root graft is to keep the branch alive until roots can form. It will eventually be removed. I don't see that there would be any difference in look between a normal air layer and one using a root graft to get over the hump. I just thought maybe if a root graft is easier, it may increase the odds of a take.

What I'll probably do is try to mix some regular air layers with my idea on separate branches. Mostly, I just wanted to see if anyone had already tried my idea. If so, I'd like to learn from your experience.

Ah, I finally see what you mean. But the main problem why most airlayerings fail on oaks is not because the branch is dying off, but because roots will not form anyway and the tree healing the branch instead. So you'll end up with a fully recovered branch with no roots whatsoever, just a nasty scar on the branch.

So unless you keep the grafted root it won't help you much. In fact, it's more likely to cause delays as it could take up to a full year or two in some cases for the grafted root to settle itself en become fully functional. Only after that could you start thinking about placing the air layer.There are however multiple proven airlayering techniques you could try out. The ring-method appears to be the most effective on Oaks.

You must bare in mind that Airlayering is an advanced skill that require exposing some parts of the tree to external influences that could weaken or even kill the tree if not properly dealt with. As Lucy said before, you'll want to be absolutely sure that airlayering is necessary before bringing these skills into play on a tree that is considered beautiful. Especially if you do not have the experience yet to perform them on one of the hardest trees to perform it on.