We can't just alternate CS-TV at any plausible amount of haste, though. We'd need a 2s CS to do that, which is well over 100% haste.
I'm not saying HA is going to be a BAD talent with t15 4p, I just don't see how the set bonus particularly favors it.
Does it really still take 50% haste to reduce the CS CD (and the global) by ~33% base? If so, I'll admit that I could well be wrong in my assumption.
But, consider: even if we can only get CS down as far as 3.4s and the GCD to, let's say, about 1.3s, a single CS>TV chain would take 2.6s which would leave us with 0.8s left on CS. As we're already delaying certain abilities by partial globals, it's possible CS would fall into that category during HA - though we'd need some of the heavy mathers to really crunch it and confirm or debunk.
Though, in thinking about it a bit more, I can see how SW would still be powerful; HoW > CS > HoW > TV would still work out well, I'd think, and that may push mastery's value up - not likely to the point of beating haste, but it may truly trump crit since that entire rotation would proc HoL.
Toss up right now, I guess, until the math's done.