Since there are now multiply difficulties of each content, do you really get motivation to run the most difficult content just for the extra ilvl? And who really cares? Back when there was only 1 raid difficulty, the reward was to see the content, to reach the X Boss, to get an item from them that no one else got (as a skin). Running in T6 was meant something, it wasnt just the extra ilvl.
So now, if you dont do mythic raid just to have fun with your friends / guild and you do it for the ilvl then you are doing it wrong. There is no Prestige anymore and ilvl will never replace that.