Blizzard will probably have to add a new difficulty entirely. While there certainly are people who would expect to be able to tackle that new difficulty if it has higher rewards, I do think some of the complaints are with something being taken away. There is a psychological difference between having content that was always out of reach added to the game and having content that was in your reach today but taken away from you tomorrow.
Honestly that’s why I think the M+ key squish was so unpopular even after we learned about the rewards going down to heroic/M0 and delves; players that used to be able to kick it with friends in a +4 might have similarly challenged alternatives and ways to get that gear, but a dungeon experience with affixes and timers at that scaling was taken away from them.