In Season Eight Rare yellow items can have three stats on them. Meaning you can add an aspect to them to make a Rare into any legendary.
I used to do this in early seasons of D4, in fact it was my main way to get legendaries. Until there was a patch making Rare yellow only have two stats.
So yeah, I don’t want to exploit, so I’m sharing that this is a possibility.
Edit: However, adding an aspect to a Rare yellow is more expensive for materials. I’m pretty sure that rule will still be present in s8.