So yes, the world is ending in 1.3 (Test server runs confirm it) but for now, I'm having fun running flags in Whitefall Steppes. Won't be much else for Rogues to do in 1.3.
I've seen several variations of capper specs for Whitefall (and Scion, I guess) and most center around Bard combat speed and Riftstalker. I went in a little different direction and have been having great success with a spec involving Marskman.
The spec: 29 Rift / 20 Inf / 17 Marks
This build goes deep enough in Rift for all the blinks and decent mitigation with Improved Rift Guard. It goes deep into Inf - all the way to improved movement speed if you're R5 or higher. The linchpin though, is the 1 7 points in Marks that give great escape potential, with On the Double / Getaway, Hasty Departure, Improved Swift Shot and Hasted Shot all boosting movement speed. Then you have Repelling Shot and Static Shot to help get some distance.
With this spec, you don't have the guaranteed full-time 20% speed like you do with bard, but with all the run speed buffs, you'll have at least one up any time enemies are around, which is key. All the additional tools at your disposal are great, plus you have some points free if you want to go deeper into Rift for a bit more survivability.
This is not a great spec for surviving a flag standoff, but for getting their fang to your base, this is a fun little spec to tinker with.