I made a thread a week or so ago about using some of the elements of Ethereals to update Primals (mostly the reduced loot pool, not the huge power boost). I really do think that the way Ethereals drop (which has been well-received by a large section of the player base) is a huge lesson for how to update Primals.
Ethereal lessons for fixing Primals - General Discussion - Diablo 3 Forums (blizzard.com)