Just a passing thought I had playing ARAM. Not EVERY item of course. But say Garen buys something like the B.F. Sword, or Blade Of The Ruined King. It'd be cool if it replaced his standard sword. Or say Ashe buys something like the Recurse Bow. Etc. Just a thought I had.
Well it's a great idea, but then you'd end up with things like this...
#Make your character "gear up" as you buy items
And have a number of custom assets, and additional gear ONLY worn by that character. So your full build self will look different than 1 item, level 1 (but full build Woad King Darius, for example would look the same no matter what items he actually built). Each skin would be different.
This would require rebuilding a massive part of the game from the ground up (Just thousands of already existing champion assets, adding in like 30-50 item interactions each....), and if ever done would have to be done in something like LoL2 or the like.
it'd probably require a lot of time and resources, but I could see a champion gaining one cosmetic effect based on an item they bought. Your example with 
works well (though 
is probably not a greatsword) and I would love to see 
holding 
.
