For alliance shadow priests, you get an extra 1% from the draenei's group buff, 3% from shadow focus, 3% from misery. You only need 17% to reach the cap, so you should only need 10% +hit. Which you can probably just socket and enchant for if you havn't hit it already, or grab the Skull of Gul'Dan or something else with a ton of +hit on it. As someone else pointed out, Sunwell loot has a surprisingly low amount of +hit on it, it has a lot of +haste on instead.
Anyway, depending on your gear, this might not make any difference at all, as many were specing away from shadow focus already.
As a random fact after 3.0 comes out we will need 17% to be "capped" against a raid boss not 16% as per today.
We get 3% from talents or require 14% from other sources. Shaman's Totem of Wrath is also getting nerfed and will no longer grant 3% hit either.
If you have a boonkin Imp. FF will grant all casters 3% and if you're alliance have have a Draenei in your party that is an additional 1%.
My understanding is there is a 17% chance to miss with spells against a mob that is 3 levels higher than you. ??? raid bosses are considered to be 3 levels higher than you for combat mechanics. However, there is always an inane 1% chance to miss with spells no matter how much hit, talents or whatever you have. Therefore to be hit capped you require 16% hit from talents and/or gear.
As it stands we can get 10% less chance for shadow spells to resist (this is the same as 10% hit, it's just stated in the negative context). meaning we require 6% from gear which equates to 76 spell hit rating (at lvl 70). For each point out of shadow focus you need to make up 2% hit, the values being 101 spell hit rating for 4/5 shadow focus or 126 for 3/5 shadow focus.
When 3.0 comes in we lose 10% hit and gain 3% hit... we can put 3 talent points into misery to gain another 3% hit (lets just ignore the fact u have to land a spell first or the fact that it can be removed or expire and require reapplication) meaning the net effect is we have lost 4% in talents. Basically this means we'll require 126 spell hit rating to be capped and you will find that most BT/SWP spriests are running at 4/5 shadow focus at least with 101 hit... so on the whole we'll have to find 25 spell hit (give or take). I think on the whole we still require a lot less hit than other dps casters, destro locks for example need a significant amount more.
On the other hand it probably stuffs around some spriests in SWP who made a decision to go back to 5/5 Shadow focus and may have sharded hit gear that problably wished they kept. In any case it makes the Skull of Gul'dan look particularly tasty for us.
Edit: I just noted above that apparently the 1% inane spell miss is being removed, if that is the case could someone please link the applicable blue post?