What GGG should take from LE

An excellent assessment and a lot of food for thought. I hope the devs at least think about some of this.

I think LE's "item editor on the low end" crafting system overall is a good fit for LE, not necessarily PoE 2, but I love the way that Legendary Potential makes uniques more exciting.
Because of the power and rareness of 3 and 4 Legendary Potential (ie the ability to craft 3 or 4 affixes onto uniques), any low to mid level unique can potentially be an exciting drop. Uniques you never would have looked twice at can become build-arounds.
The closest comparison is the way that sometimes 6-link unique chests or 2-handers can drop in PoE 1, which I miss in PoE 2. But this is much better.

Of all of LE's systems, I think this or something like this would be the best fit for PoE 2. Let's give every unique the small chance to be very powerful. Of course it greatly raises the ceiling on the already powerful uniques, but that's fine.