Very interesting! So a lack of O2 is another thing that will drive PH up.
Now that one is also interesting. I have not read it yet, but it sounds like they are talking about an NFT rail system - like the ones in gutters or plastic pipes - where the plants are essentially in a long line where they all see the same water one after the other. They seem to be saying that the plants that are first in line get good O2, and the ones further down the line get less and less O2. That makes sense to me.
I dont see how that would apply to most other types of hydro though - like Flood/Drain or DWC. RDWC could also suffer from the same effect to some degree though if the aeration is all in the control bucket.
So far, everything you have found indicates that maintaining good DO levels is a critical thing to keep in mind in hydro.
I cant help thinking that it has to be just as important in soil grows. The general recommendations to not over water and to have soil that has good drainage, and can breath well (good aeration) are as important as folks say.
Another excellent find!!