I think it would be about the same size of shitstorm as the one the people who had execs essences and ditched the quest since they had no more use for those after upgrading all legendaries would raise.
I'm pretty sure it wouldn't be a first time they delete/convert existing currency to something else.. gold for example.
I'm also saying this because last month on eu forums blue [Tizaksul] said the following to a person asking for any other uses for the esssences:
"
Once all of your older Legendaries are level 1000 you no longer need the quest. Any new ones that drop for you will already be item level 1000
The Wakening Essences will only drop for you while you have the quest in progress though, if you've already upgraded all your Legendaries, hand it in one last time and you won't need it again "
Would be a super duper dick move to say that on official forums, make people drop the quest as unnecessary (me included) and then bit later say "why did you drop that quest you should have used the this time to stockpile"