What this means is this Hunters may become the new anti-Druids in the arena, and may especially find a good place in 2v2s and 3v3s to counter the dread Restoration Druid. One of the big complaints about Restoration Druids is that when the going gets tough, they can Cyclone their attacker and run off to the other side of the arena using Travel Form, or else shift into Dire Bear Form and weather the hits until their teammate can CC the attackers or otherwise divert the attacks.
Instant-cast Scare Beast seems to be the perfect counter to this tactic, since a Hunter can instantly fear them, and the 20 yard range on Cyclone means a Hunter can stay out of Cyclone range while still being able to deploy Scare Beast, making a Druid think twice before shifting at long range. Restoration Druids will certainly have to be quite a bit more wary of Hunters. They should still be able to use line of sight to great effect, but at the least they'll probably have to save their Cyclone usage for the Hunter, and they'll find it a lot harder to run away from a Hunter.
It also means Feral Druids will have to be more cautious around Hunters. Since they need to be in feral forms to do their damage, they'll be constantly vulnerable to the spell. I will say, however, that as a Feral Druid, I have been consistently able to destroy Hunters in the past, so I don't mind as much that Hunters have a tool against me. However, in the interest of full disclosure, I should note that I also play a 70 Hunter and thus may be biased there.
It looks like Blizzard is definitely working at balancing out Arena numbers, as this change seems tailor made to counter one of the most over-represented Arena classes, and is being given to one of the most under-represented Arena classes. It should be very interesting to see how it shakes down.