I do think that there is a lot that a long liner can take from Seth's video, and it isn't where the edge change takes place. I agree with those that said you can't just do what Seth is doing.
I think what can be gleened from the video, is just how easy the correct body position (after the turn) makes getting across the course. I am always amazed at how hard, fast and ineffective many long liners are. There are plenty of strong, hard turning, waterskiers who work extra hard but struggle with 15 and 22 off.
Getting the hips/handle to the correct spot after the turn, getting stacked and having arms extended and close to the body. Establishing lean away from the boat etc.
My take on it, is that the more lean away from the boat after the hook up, the earlier the edge change will naturally occur.
In the end, the long liner will be doing this all later than Seth, but they could (with good instruction) emulate good body position, handle control and lean. After all, they don't have to ski as well as Seth to get through 15 off.