Blizzard should keep Artifact Challenges after Legion, but with a particular restriction..

.. you're level-scaled to 110, and your item level is capped at 1000, or whatever Legion's maximum will turn out to be after BfA's stat squish. Any consumables will be limited to ones available during Legion as well.There, now they can all remain exactly as difficult as they are now, forever, and the content doesn't have to get removed. I'm fine with certain other changes, like a particular raiding mount's removal, because the precedent for that was set all the way back during WotLK, and it's just one item, not an entire system tied to EVERY single classes' multiple weapons and subsequent unlock grinds. Content removal sucks, period, and not being able to do them all because you focused on other things (or simply did not have enough time to do it all) is rather lame.And if THAT still annoys the elitists, then make it so you can only use these artifact appearances as transmogs in BfA if you did it prior to that expansion, based on the date when you earned them. But please, I'm begging you Blizz, don't remove this stuff entirely, as it's a bad idea and unneccessary if implemented as above. You've got the scaling now, so use it for this in a post 110 world.