Now, we do want Subtlety to be more attractive. All of the pure dps classes have a spec that isn't as popular as the others. Mages may be the closest because at least Frost has a viable PvP use, but there are also plenty of mages who want to be able to use Frost in end-game PvE too.
Subtlety (and Frost for that matter) are specs focused around utility. The problem is that players understandably nearly always choose damage over utility for raiding and often choose utility over damage for PvP, unless the damage is really high or the utility just doesn't cut it for some reason.
What we are talking about doing is sharing more of the utility among other specs, or the core class, so that there aren't "utility trees." To do that though, we have to make the way the different specs do damage different enough so that players might choose a play-style preference over highest damage. This is particularly challenging for rogues, who have a history of giving up a preferred spec or play style for one with a sub 1% dps increase.
I think we are closest with the Arcane vs. Fire mage specs at the moment. They play a little differently, which goes beyond just the type of magic damage they do. While Fire might still do the highest damage overall, Arcane is close enough and plays different enough that even competitive players don't feel stupid for playing that spec. There are a lot more Arcane mages out there than I think a lot of players assume.
That is harder with rogues. "I'm the sneaky one" doesn't translate into sustained raid dps. Assassination feels like it emphasizes poisons more and Combat feels like it emphasizes weapons more, so we're a little closer there. Subtelty needs a stronger yet damage-oriented niche.
HaT, sadly, is not a niche. HaT has scaling problems. It's appropriate for a 5-player group, but gets too in larger groups with all of their raid buffs. We don't want HaT to be the one talent that pushes players into Subtlety.
they shoulda just left hat broken and forgotten about rogues.