Have you ever read Blizzard's patch notes and wondered exactly where the developers are going with certain changes? We're all familiar with the fact that subtlety has been lagging behind the other rogue specs in DPS. It's actually still seeing some use in top guilds on healing-intensive encounters, due to Enveloping Shadows giving us nearly permanent Feint on top of 30% AoE damage reduction. The fact remains that subtlety has largely been a PvP spec outside of very specific situations, although it's a quite potent PvP spec. The patch notes show us that the developers obviously want for subtlety to be more competitive in PvE -- no surprise here.
What I don't understand is the new Blade Flurry mechanic. On the PTR, Blade Flurry no longer has a fixed duration, meaning that you can have it up 100% of the time. While yeah, it sounds awesome, it also opens up huge balancing issues. It means that any time there's a raid encounter with more than one target, we're stuck swapping to combat. There are plenty of other classes with similar Cleaving abilities, but none as powerful as Blade Flurry. While I'm all for spec diversity, I'd rather not waste development time on something that's certain to be cut once it makes it to live.