It isn't very balanced, it's either too powerful if you chain two spells back to back (such as smoke bomb in the case of rogues) or it's poor if you need to use an ability right now to stay alive, but it only has a few seconds left until it's off cooldown. Because some abilities are able to be used twice, they end with their original potency being nerfed, which means that the ability is now less powerful for all the talent trees except the one with access to preparation.
I know some people are going to complain that for them it's very effective and they don't want it to change. But in my opinion by having spells such as this, for the sake of balance the class has to be weaker in other areas, which means that the one talent tree with that cooldown that refreshes cooldowns, becomes the default pvp choice.
This is only my opinion, which I'm free to express even if you disagree with me, but overall I think that it is a bad design. Rogues have always relied on preparation in pvp and sub has always been the default choice because of this.
In tbc, a vast majority of rogues went sub for pvp. Assassinations wasn't very popular at all, it was more difficult /annoying to play and didn't always pay off enough in the damage it could provide. Sub was very common, as was the "HARP" build before it was rightfully nerfed. "Hemorrhage Adrenalin Rush Preparation" was a combat/sub hybrid which meant that you could perform back to back adrenaline rush/evasion and spam Hemmorhage every second for 30 seconds. This is an example of being over powered due to preparation.
During wotlk, everyone was running around with variations of 41/5/25 so that they could take both preparation an mutilate because the 51 point talent assassinations tree (a clunky and boring active 15% damage boost for 60 seconds with no cooldown and 100% up time) wasn't as useful as preparation and the early sub talents. People rarely speced into sub because the damage simply wasn't as good as what assassinations could offer. Combat did, and still does, lack the control, mobility, and burst (outside of cooldowns) to make it useful in pvp.
Before cataclysm talent trees, a few people occasionally speced into a "coldstep" pvp build, which meant picking up preparation, shadowstep, and cold blood. It wasn't really over powered, especially as you had to give up shadowdance or mutilate, but it was somewhat entertaining to play for change and to be different. It was moderately effective because of preparation resetting cold blood, although crit's weren't that much of a big deal in wotlk because by the end of it everyone scaled poorly and was pvping in pve gear because burst was so high.
The point to all this is just to say, that I really think if rogues have yet another expansion where they are balanced around preparation, they will continue to spec subtlety as a default, which kind of destroys the whole point of creating the option, or rather the illusion, of talent tree choice.
I think that the solution to this problem would be to remove preparation, but in return shorten base some survival cooldowns across the class by perhaps up to 50%, or less desirably double their duration or potency depending on the ability in question. This would prevent rogues from being able to chain certain abilities such as smoke bomb one after another.