GC actually tweeted about this recently, he mentioned UH/Frost's usage of melee weapons as barriers to realizing your second potential solution. He didn't address your first postulated solution so no comment there, other than I can't initially think of any downsides that can't easily be accounted for. {Edit: agreed, Shaman indeed to look stupid as hell. I gotta say no thanks to mail gear on my Holy Paladin unless it looks the exact same as Ret/Prot gear, which would mean a bunch of confused Shaman would be running around looking like Paladins haha. I don't see this happening, sorry man. Good suggestions though}
I really don't see a problem with Int plate as a whole because I feel like its presence doesn't constrain loot tables enough to warrant violent changes to how some class/spec works. GC said a while back that they would like to do away with it, but right now there isn't a better alternative than just letting it be.
Maybe a spec or two of Demon Hunters will use Int plate once they get added to the game
That is, if demon hunters wear plate at all lol