Ive been using BoS on live for a while now, to me and my friend who is also a longtime rogue its what sprint should have been from the start. I will definitely be sticking with it come 5.4 but I'd much rather they properly buffed shadowstep, its a way cooler ability that just screams "shifty, attacks from the shadows" type character and rogues SHOULD be in your face most of the time, but the CD is still too high even with the buff.
Shadowstep is a very solid move though. Because it is instant, many of the weaknesses of other gap closers are not present. I'm ok having it be for trade with burst of speed. If sprint had been burst of speed (and the burst of speed change was pretty much a suggestion from the forums back in the day), then it would have been our gap closer. Sprint was always meant to be a battlefield position tool though- very rarely do you effectively trigger sprint to close a gap, and this has always been the case.
I actually think that tier is one of the few talent tiers that does what the devs said the talents were for. With the exception of the dumb teleport-on-open one.
Well, I think Burst would have to literally be free before YOU would consider it.
Burst of speed is already top notch for RBGs, as it allows for the fastest stealth reposition in the game. It's already a solid pick for any arena comp that will involve two melee on you (granted, we don't have many viable teams that result in that, and cleave is an uncommon composition to face in this Hogwarts season).
The shadowstep buff is substantial, but burst's buff is much larger. I think you are underestimating how much better this move is getting- I believe it will be undercosted by a little bit in 5.4.