You should not be allowed to roll Need on loot that your class can't wear, period. It blows my mind when players roll Need on stuff that isn't for their class... my mind has been blown even further by the fact that players have been asking Bioware to change the roll priorities on loot since beta and they haven't fixed it yet.
The only thing they have to do is limit Need rolls like this:
Guardian/Juggernaut - roll Need on Heavy Armor with Strength only.
Sentinel/Marauder - roll Need on Medium Armor with Strength only.
Smuggler/Agent - roll Need on Medium Armor with Cunning only.
Consular/Inquisitor - roll Need on Light Armor with Willpower only.
Trooper/Bounty Hunter - roll Need on Heavy Armor with Aim only.
If the armor doesn't match your class Need table, then you can only roll Greed. Then, you're only fighting with dps vs. tanking and dps vs. healing gear rolls. I think that's astronomically better than rolling Need on loot for your companion that you don't see anymore post 50.
I don't think this is a great idea. Suppose a random piece drops, and its a medium armor with strength, but you are the only one in the group with strength mainstat. You are unquestionably entitled to need on it (assuming you do need the mods), but this system would prevent you from doing so. In addition, in most cases it is the mods that matter, not the orange shell. Whether the armor is heavy or medium is really irrelevant. An example for this: a heavy armor piece with dps mods should clearly go to a mara over a jugg tank. If there is a jugg dps and mara, and both can use the mods equally, it does not make sense to give the piece to the jugg only because the shell happens to be heavy.