Since Earthquake's quite useless (apart from its knock down) and only really used with Ancestral Swiftness I think it would be a good ability to speculate on what it could become. With the state it's in now, I wouldn't be surprised if it was removed or completely revamped in 6.0.
I thought of a nice idea awhile ago that would make it more of a utility ability instead of an area of effect damage cooldown. Something along the lines of...:
30 yd range
1.5 sec cast, 30 sec cooldown
Breaks up the ground between the caster and the targeted location, causing it to erupt in a spike of earth after 3 sec. Enemies within 5 yards of the erupting spike, or who have walked into the travel path of the rupture line will be stunned for 4 sec.
That's basically it, but in my opinion it would be a pretty cool idea and make sense to be for an Elemental shaman; not to mention some of the interesting strategies players could utilize.
We just have too few Earth-based abilities and Earthquake is useless as it is.