Do YOU think we'll get a new Tank and/or Healer in 4.0? And vice versa.

[SendohJin]

That said, there are different types of dps: melee, ranged, and magic. We don't have that yet with tanks and healers, so the 1:1:2 ratio doesn't necessarily have to be enforced as far as having different classes go.
Personally I'd like to see another ranged dps class. One who isn't a 'support' type.

The ratio is 3:3:4:3 Tank:Melee DPS:Ranged DPS:Healer

you want 4:4:4:4 so the missing ones are Tank, Melee, Healer.

that would work for balancing Light Parties and Full Parties.