[MENTION=1465]Li Shenron[/MENTION]
I agree that Bard, Druid, Ranger, and Sorcerer could use one more subclass each, not for symmetry reasons, but for full coverage of what are now common character concepts.
For the Bard, it appears the College of Wit from the playtest has been dropped? Man, vicious mockery was a thing in 4e! The smack-talking social hero seems apropos for bard, with only a bit of overlap with the Rogue's Arcane Trickster.
For the Druid, it's possible the Circle of Land *is* the spells-focused "weather" Druid. I was thinking Swarm or Blight Circles might be interesting.
For the Ranger, I personally love your idea of a Planewalker Ranger, but I suspect something more "classic" might have greater traction. The way Hunter is described, it almost sounds like the original ranger from White Dwarf IIRC who was a frontiersman modeled directly on Aragorn. However, the name Hunter implies that it is probably the "favored enemy" build, and if that's the case then there could be room for a build based on the original ranger.
For the Sorcerer, there are so many options for other lineages! Dragon and Wild Magic are great, but something that is a little more accommodating of different character back stories would be great too. Something like an Elementalist pops out as a common archetype that isn't explicitly covered.