One of the major flaws of Azerite was the issue of having to farm for the same traits that you already had just at a higher item level. How is this any different to Mythic+? Every season you're simply farming for the same gear that you already had just at a higher item level.
I don't feel like the current Mythic+ system is very sustainable in the long term. It needs a drastic overhaul and fast. And this problem has been made far worse with the gear normalisation between dungeons and raids and the introduction of seasons in BFA. As soon as people realise that their character progression in the next 18 months is simply going to be farming for the same gear in the same BFA dungeons, I think that interest in the system is going to die out.
I can't imagine the M+ loot carrot lasting beyond BFA as the system currently stands.