Im not sure what this change accomplishes. All it does is turn legos into rares with more aspect juggling to do. Why do rares have to mean something? We already have a loot progression from blues to rares to legends to legends with uniques and mythics. This solves a problem that doesnt exist.
To improve itemization here is what should happen.
1] White and Blues removed from game. If one of these would drop its now a rare.
2] Legacy Mythic items dont exist. Mythical Items that are changed become the new versions.
3] Items drop less but ranges are tightened up. Example Starfall Coronet has a range of 4-10s just for the main stat. This would be changed to 4-6s.
4] Alternate art cosmetics mythics added to game. This gives players with the D2 super rare loot hunt something to go for longterm. 1 in 500 mythics are alternate art.
5] Items can no longer brick and you can keep a previous roll just like enchanting. Manuals are fixed to prevent bricking. Tempering 2.0 
- PC General Discussion - Diablo IV Forums (blizzard.com)