this is the first thing they are introducing since legion launched that wont be changed down the line. glad they are learning.
to explain what i mean, they added mythic dungeons (nothing but glorified heroics) and locked them out of lfd, they will change that.
they made AK char bound, they changed it.
they made legendaries have a cap on BLP, they removed it.
this change means people will get those upgrades for they main and their offspecs eventually, even on alts that they only have time to do LFR in.
the one thing that still puzzles me is why they didn't do this from the start... ALL legendaries should have been available to all players at 110, but being low ilvl 835ish or something, and have them upgradeable with the upgrade time linked to the content you do. and done, players now get to CHOOSE which one they like.