I think the mana that'll be returned from Serendipity will be much more than 10% less mana on instant cast spells. Also the Imp. HC on beta servers (60% haste, 3 casts) simply rocks. With 16% chance on clearcasting this effect is running almost all the time thus granting fast, big heals that will return 60% of their cost when they overheal for more than 50%.
Unbreakable Will will most likely be a shame to lose for some encounters. 15% extra fear resistance when killing Archimonde is really great. Though i have to say that with Fear Ward up and Insignia (+ Totem) i rarely noticed the resists from this talent. I think we can afford to pick Twin Disciplines instead.
This is the exact spec i already posted. Do you agree that you'd use it too or did yo maybe just have the wrong URL in your clipboard? ;>
Either way you don't need any spell haste at all with the spec i posted. You will be granted 60% haste on the clearcasting proc - which happens to occur quite frequently. 60% is really more than enough :>
Most likely this, but depends on them getting ranks right for penance and/or fixing borrowed time, since atm its not worth the points compared to other talents (and especially not the position in the tree). Hopefully the spellpower to inner fire is retroactive once live since its a waste for pve to have the points otherwise.
Now that is an atrocious spec. 45 points in holy without CoH?
Anyway I think you're confused as far as Imp. Clearcasting goes, based on your haste comment. You don't need any haste to make this talent work, all it does is increase the casting spead of your next spells by 60%. It is not a 60% increase to your haste value.
Edit: I also agree that Twin Disciplines is superior to Unbreakable Will.
I've seen no reason to believe they will remove the downranking nerf. Serendipty will likely be a must.