Zoe's W is what a lot of people like to complain about on her. It's a very powerful spell, and the spell that I would say defines her.
Her R, on the other hand, is basically just a glorified basic ability. As it is, it's just a blink and a blink back. To compare, Leblanc has a very similar ability as a basic ability, only with her she not only does a ridiculously high amount of damage with it, her blink-back is optional.
I think if Zoe's portal jump was moved to her W, and her spell thief was moved to her R, it would make things a lot better. It would make her weaker pre-6, at least in the "get ignite/protobelt/redemption as a free drop and win" department. It would also allow the ability to be budgeted more towards an ultimate ability.
Just as an example, here is how I would change them:
W: Portal Jump
Cost: 50 Mana
ACTIVE: After a brief delay, Zoe dives into a portal that she opens beneath her, blinking to the target location.
Zoe remains able to attack and cast abilities during Portal Jump, but is unable to move. After 1 second, she falls back through the portal and blinks back to her cast location.
R: Spell Thief
Cost: 1 Mana (like Taliyah Q on worked ground)
Cooldown: 0.75/0.5/0.25 seconds
...(same as current W)...
PASSIVE - WHEEEEE: Casting Spell Thief or one of her own summoner spells grants Zoe 30/50/70% bonus movement speed for the next 2/3/4 seconds, and summons three bubbles that orbit her for the next 10 seconds. The bubbles autonomously hurl themselves at the nearest enemy in range, prioritizing her attack target, dealing 30/50/70 +15% AP magic damage each. NOTE: Bubbles no longer apply her passive.
Let me know what you guys think.