Holinka gets it
In his comments about Shadowstep, Holinka isolates why Shadowstep is so good: "instantly on target." Positioning on the map is simply an abstraction from "can we attack our current target right now?" A rogue doesn't care if he's fighting on a bridge or in a river or aboard a boat. All that he cares about is if his target is in range of his blades and poisons. Maximizing your uptime has always been the best way to improve DPS in both PvE and PvP for years.
Holinka goes on to mention Crippling Poison and its associated Shiv effects in his next tweet. Why would our slows have anything to do with our mobility? Because slowing our opponent allows us to increase our uptime, which is our eventual goal. This isn't World of Track and Fieldcraft, it's World of Warcraft, and our goal is to bury our daggers deep into our opponent's ribcage. We don't need to win a footrace, and in fact rogues do some of their best work when standing still. Mobility is simply a means to an end, and that end is improved uptime.
Stuns, slows, and shuriken
Rogues have a wide variety of tools available for increasing uptime. Cheap Shot and Kidney Shot give us several seconds of uninterrupted time to unleash our cooldowns. The Glyph of Cheap Shot is so popular because it lets us squeeze a few more attacks into that uptime window. Many rogues are using their two-piece tier 15 set bonus to extend Kidney Shot's duration by an extra second. Cloak and Dagger would be pointless if we didn't have Cheap Shot to freeze our target in one place.
Shuriken Toss has been a boon to rogue PvP because it allows us to maintain a relatively high DPS uptime even when we're being kited. There are two types of class in WoW: melee and ranged. Melee classes are going to want to go toe-to-toe with a rogue, and ranged classes desire nothing more than to stay 40 yards away. The cat-and-mouse dance between rogue and ranged has always been a point of balance contention, and Shuriken Toss jumbled the whole thing up. Frost Nova or Entangling Roots are no longer capable of nullifying our damage. With Shuriken Toss, we can maintain uptime at long range.
A monkey on the back
I would gladly trade Shadowstep and Sprint (in PvP) for a Killing Spree-like ability that let me hop onto an opponent's back and attack them continuously for 15-20 seconds. If you give me 20 seconds of solid uptime, I'm going to deal a lot of damage. I'll always be in range to kick my target's spells and all of my attacks will land. If I didn't have to worry about stuns or slows, I could pour all of my energy and combo points into raw damage. A 20-second burst window would make rogues an unstoppable force in the arena or in a battleground.
Shadowstep and Sprint are just pieces in the larger game. We use Shadowstep, they use Frost Nova, we use Kidney Shot, they use Blink, and so it goes. What rogues want, and often have a hard time vocalizing, is to be attacking their target more often. Mobility is seen as the easiest way to achieve an increased uptime, but often it comes down to using our other abilities more effectively. If we're pumping our targets full of Crippling Poison via Shiv and syncing our stuns with full energy bars, we'll have all the uptime we'll ever need.
Uptime is king
The goal of a rogue in PvP is to get enough uptime to kill a target. Sometimes we'll be using our abilities to provide uptime for our allies, and other times our teammates will set up opportunities for us to unload our cooldowns in an uptime window. If we use our mobility skills to close the gap, then so be it. If we use our stuns and slows instead, that works too. Rogues don't need to be the mobile class, but we do need to have the combination of abilities that allows us to obtain the uptime numbers needed to score a kill. Shadow Dance isn't any good if your target is running away.
Sneak in every Wednesday for our patch 5.2 guide, a deep-dive into the world of assassination and combat rogue AoE rotations -- and of course, all the basics in our guide to a raid-ready rogue.