My table's rule (partly created because of the Ruby of the War Mage) is that if a weapon can function as a focus, it must be either
A. Affixed with a Ruby of the War Mage
B. A ceremonial weapon. A ceremonial weapon is an improvised weapon dealing equivalent damage to weapon it's made to resemble. If the character critically fails while attacking with it, however, it breaks.
I haven't read this thread, I just wanted to add what my rule is. Apologies if I'm retreading already covered ground.
Edit: Also apologies for the thread necromancy. Totally didn't notice.