Perhaps you could go with a line of ninja, or samurai weapons. Like a katana, a ninjato, a shuriken, etc.

I think these would sell, do to the Ninjago theme.

katanas have already been made by lego but a realistic shuriken would be awesome

Not saying that this would restrict BF from making their own, but MinifigCat has made some pretty cool ninja/samurai gear. Including what you have asked for.

I must check that out sometime. Thanks for the FWI.

Funny thing about ninja type items......sometimes you just get ninjaed.