This is a suggestion that may gain support with all the recently enraged players.

Unlock all the items (or maybe only 4* and 5*) that were made before the update. Do this as a one off.
The major complaint I have read (the only one I really agree with) is that no warning was given before implementing such drastic change.
If you let people sell/give back the equipment they never had any intention of using it might go some way to easing peoples anger.
Some of the other changes might not be liked but I think people might wait and see how the new economy works out rather than quitting.

As the games creators and developers is there no way to unlock all them items that were made before the update?
I'm not a coding expert but surely that is possible. If no data is kept on each item for when it was made just do all of them.
The players that want to continue using them can re-bind and the other items can be fairly returned or sold in their present state.

Some soothing measure may save you a lot of customers!

others include
A roll back to give people time to adjust
a method of un-binding items in game that has a cost of crowns or CE

The major mistake was a lack of warning!

Players please post to show support