Couple things wrong with this assumption:
1. Blizzard is notorious for letting PTR stuff go live as it was introduced on the PTR. In fact, 90% of all things on the PTR go virtually unchanged the moment they are patched in for testing. Even some major bugs and design flaws go live.
2. We know how things are scaling because we've done extensive research on the PTR. That's why I linked the spreadsheet in the first place. Knowing Blizzard, those numbers are going live and will remain unchanged for several patch cycles (until Blizzard gets around to fixing the extreme outliers).
Now, from the current PTR numbers, here's what's going to happen: MOST enchants we currently use prior to level 60 will remain BiS. Stuff like 15 agi gloves, 15 sp bracer, Stam to chest, Crusader, ect. What will change are enchants that confer a benefit not currently available to low levels (IE, power torrent, agi to bracer, int/crit/str to cloak, expertise, leg kits, shoulder kits, ect).
That's the other reason why I linked the spreadsheet. Any player making a twink right now can give that spreadsheet a once over and decide which enchants will still be BiS in 5.4 they can currently get now, and then also get the new ones which will be BiS in 5.4.
But just saying 'wait and see when 5.4 hits' is kind of telling players to waste all this prep time and then fall behind once the patch finally comes out. The data is there, no reason to avoid doing the work now.