@Riot: What are your thoughts on an anti-tank assassin?

Assassins primarily have one role: kill squishies. Between Rengar, Talon, Evelynn, etc., there's little deviation from that. Now, since marksmen were reworked to each be more unique, I say assassins need someone who breaks the mold and goes instead for heavyweight targets, not squishies.

How could this be done? Well, you could have this Champion deal % health damage, give them less burst in exchange for DoT, make them CC-resistant, etc. But those are just basic ideas. You'd need to get some really cool mechanics together to make something like this work. But if it were made, it'd certainly add new levels of strategy to the game by enabling your assassin to pick off that annoying Rammus or Nautilus before a teamfight breaks out, leaving the enemy team's squishies wide open for the rest of your team. But at the same time, send this assassin against a Graves? Expect to get blown to bits.

Is this doable? Or does it result in "Burden of Knowledge" errors for the players?