The idea of 100% has been raised a few times. The main problem is there's just so much stuff. If it's -really- 100% then you would need to get all items, including 1/128 drops. While it's certainly doable, it would probably take a really long time. Even if you allowed glitches/manip in a 100% run, it would still take forever. Sword of Kings alone would likely take anywhere from 1-3 (or more) hours to find.

This discussion goes all the way back to the early days of SDA (https://forum.speeddemosarchive.com/post/earthbound.html).

The same ideas you presented were mentioned along with some more ...interesting things like visiting every area in the game and talking to all NPCs. Nobody could agree on anything, and the consensus was that nothing is really tracked by the game so why do it or why put it in the 100% category. Because there are so many different opinions on the matter and it has been in discussion for years and still doesn't have a run, it will probably never become one. The rare drops can be cheesed with RNG manipulation. You could use the debug menu to put all levels up to 99. You could use the item duplication glitch with rare candy to force everyone's stats to max. You can clip out of bounds to the item drop areas quickly. It breaks down quickly and becomes a wonky run which many people don't anticipate.

Note that this doesn't mean you can't try something like this out. By all means, have fun with it. All it really takes for for a run category to become a thing is one person doing it, people seeing it and liking it, and additional people picking it up. I could easily be proven wrong here (but my money's against it :D)