It would be really cool if boss drop weapons could give us their animations and themes, just for their critical hits. It would be a lot of work to make animations for each and every attack on a boss drop weapon, but if they just got a player version of their criticals and gave it the critical theme, that would be awesome. If Axe of the Minotaur Lords made you do a Minotaur critical animation, it would still have the same Vicious Charge, Assassin's Strike or just plain basic attack animations as a Big Choppy weapon. Something less likely to happen would be the Tubthumper giving you Mormo's strange criticals.

Also, another thing related to this topic:
With the Primitive Greatsword having no weapon type, it would be cool if it could be stitched with any melee weapon. Blades of Shade with the appearance of that thing would be pretty cool for my Swashbuckler with Cool Ranch Witchdoctor clothes.