I use burst of speed almost exclusively at this point, even on fights where shadowstep is better. I think I swapped on a couple fights where step really provided a solid strongarm, but in general, I find that the entire removal of "woops I stepped into bad" more than makes up for the trivial dps loss, and simply never having to think "I'm out of juice" is soooooo nice. Then there's the debuffs it can clear. Huge fan of this move personally, it really feels like they nailed it. When there's two choices and I strongly prefer one without having any issue with the other, then that's the rare time of the talent done right.
And no, I don't want to lose sprint. See, I have button, semicolon (would be where z is on your keyboard) this is my gap closer on like eight classes over three games. It's shadowstep if I spec it, and it's burst of speed if I spec that (it changes automatically with infmoptalent whatever that addon is, or Ari wrote a weakaura).
Then sprint is 0, which is also nicely mapped on my mouse. I use and love both. Your way wouldn't even save me a button! Unless shadowstep was baseline with a two minute cooldown or something, then I'd love your method as the talent tier would basically become "greatly improves one of your mobility buttons". But I doubt they would do that sort of thing.