How exactly will this work? If a character has already upgraded an epic piece to a legendary epic piece, then the player buys a golden epic card, what happens? Does the legendary epic get replaced by the golden epic, or does the legendary epic get replaced with a golden legendary? If the legendary epic is replaced with the normal golden epic, do the crafting materials used to create the legendary epic get refunded? Whether or not the materials get refunded, does the material requirement for epics/goldens for all crusaders revert to it's prior iteration (from 5 down to 3, etc), or does it stay raised?

there is no legendary epics.
there is epic, golden epic, legendary, and golden legendary.

I sent a ticket addressing that question. Here is the response Erika gave me:

Hi atlm,

Thank you for getting in touch.

If there are players who did experience golden legendaries getting replaced, they really should put in a support ticket.

If you own the Legendary, you will be offered the Golden Legendary, as you can see here with Panda and her Pocket Watch. http://prntscr.com/ekdbcm

If you just made the Legendary, you will need to reload the game to update the chest store or flash sale to show you the Golden Legendary version instead of the Golden Epic version.

But even if you don't reload, when you buy the gear and receive it, you will see the Golden Legendary on the chest opening screen, and when you hover their golden legendary on their bench spot, it will have the correct levels.

What could be causing confusion for players is the order of sorting on the bench of items.

The order changes when you have empty spots, when you start getting golden epics, and then again when you start crafting legendaries. That is on the player suggestion list to be more consistent about.

Hope that helps.

Best,
Erika