Knew I was forgetting one /facepalm
But yeah it's entirely possible for them to put in something other than a weapon as a legendary, but I think that'd break the pattern Blizzard appear to honor almost as much as... I don't know... Hitting mages with the nerfhammer.
Also, if you were to get a legendary weapon, it'd be almost impossible to replace, however a trinket could fairly easily be overwritten depending on the tank's own style of playing or what he/she's needed to tank.