Haste becomes more valuable for us because of a lot of reasons.
-It'll be our spec specific 5% boosted 2ndary stat, of which every spec has one.
-EotE procs of pretty much everything, so more haste => more procs => more SS/LLs
-new Flurry makes haste reduce LL/SS/Shock/FN/UE cooldowns, as well as the gcd. No idea wether they'll include EB in that
-Haste increases the amount of FS ticks, which will be able to reset LL cd
And it indirectly becomes more valuable through mastery becoming irrelevant for Ascendence. Mastery will still be good for Shocks, aoe in general, LB/EB and LL though, just to name the most important. Especially considering the amount of LLs we will have with FS ticks and new EotE, and also stuff like Liquid Magma or Elemental Fusion, it is very hard to say just how good mastery will be, especially with the number pass yet to come.
Basically the more of our damage is contributed through elemental damage, the more worthwhile mastery will be.
There's a thread surmising about the highest benefit. Personally I think Haste > Mastery/Agility > Crit > Multistrike/Versatility, based on nothing than a gut feeling, as I haven't played for a while, nor have beta access.
One thing's for sure, they definately didn't slack in trying to make enh more fun playstyle-wise. Now if only they showed the same vigor in pvp design