One of the players in my old game was a 10th level mage (well, 6th with 4 levels of scion I believe) that has the two handed sword that's a dragon bane blade.
In my old campaign, one of the players had such a blade, a greatsword, but never bothered to get it identified properly so it wound up in NPC hands.
I've used several NPCs with those items as well.
This is one of my favorite versions of the 'rising' in power style item.
For an alternative take though, in the same campagin with the mage, one of the other characters has the feat, Item Familiar, from UA and enjoys that.