As for relics/rare equipment.

Since we have such a diverse crafting system, they could do something such as each boss randomly drops a part for some kind of special equipment. all his drops are special equipment drops, the one he drops is random.

Then there will be other bosses that also do this.

Eventually if you can obtain all of the parts for the item, it can be crafted/rebuilt into it's original super awesome magical form.

E.G/
Boss 1 - Excalibur handle
Boss 2 - Excalibur blade
Boss 3 - Excalibur grip

Synthesis handle + blade + grip = Excalibur sword.

The only problem is if you haven't levelled the craft required you'd need someone else to do it, then there'd be the problem of it may become untradable when created or the crafter may steal it. Can't think of a way around that problem yet though...