I understand that Blizzard is trying to rebalance combat to be PvP viable. I don't agree with doing so...I think not one but TWO jorm...er, PvP viable rogue specs are quite enough. But I understand what they're trying, at least, to do. Even if the costs it's taking on combat in its primary role as PvE dps are a bit troublesome.
As a part of this, the current state of Blade Flurry is well...odd. It's cumbersome and unwieldy in a lot of circumstances. I'll give a for instance.
I'm in an instance, and the tank pulls two sufficiently chewy mobs at once. I go in and pop BF. Only...ut-oh, here comes the mage with a lucky crit string. Bam bam bam, first mob dies really fast. Now I'm down to one mob with BF active.
The problem now, is in that BF has had both the haste buff removed, AND been saddled with this odd energy regen nerf. The result is that on a single target, not only is BF not benificial, it is actually a DPS NERF to have it active. Therefore if other targets die faster than expected the only way to keep your dps running 100% optimal is to reach up and click off the BF buff. It's odd, it's unwieldy, and it's just plain become an ugly hack of a mechanic.
There's a few routes you could take here. You could re-introduce a haste buff sufficient to not result in a net dps loss on single target. (From what I'm hearing combat could now use some buffs anyway). At the very least you could make the energy regen nerf dependant on actual 2ndary attacks landing on targets, or just remove the energy regen nerf completely. Just get it to the point where I'm not having to click off a buff midcombat just to keep my dps max'd.