I'm worried that 2/3 in pain & suffering won't cut it purely for the 10% SW
backlash reduction, now that we crit a lot harder the backlash needs to be mitigated. Might prove to be trivial but I have SW
myself for 4.5K in TBC before, so once you factor in the dps increase it's gonna start to sting.
I think 3/3 in shadowweaving is going to be a must, we want to cast SW:P with full stacks as early as possible so it refreshes for the maximum damage over the course of an encounter. It's also down from 5 points to 3 to invest in and I think it's going to be worthwhile.
I'm not so sure that 3/3 in shadow affinity is a must... we are going to get an innate 30% threat reduction from Shadow Form, so we're already well ahead of the pack when compared to the other dps casters. In addition the new VT mechanic means the threat is going to be attributed to the person gaining the mana, not the spriest as it currently works. So with all that in mind we might be able to steal a point but like you, i'll reserve judgement until I experience the content.
Meditiation & Imp Spirit Tap should stack, this type of mana regen mechanic has always stacked so unless something has changed that i'm unaware of expect it to stack. Now that spirit is going to be itemised on gear even more I suggest that Meditiation is going to be a must... you'd take meditation over points in focused mind imo... im sure when we get a feel for what sort of spirit we can expect some models will show meditation will be vastly greater than focused mind.
Now that we need to reach 17% hit from talents/gear and lost 4% overall hit in the tree (basically we're down by a net 5%) I think you're always going to take 3/3 Shadow Focus, it also reduces shadow spell cost by 6%, it's always going to be a good investment for your points.
Looking at imp inner fire again, you might steal points from this to place in more important talents in the shadow tree when it makes sense. For example if there is content with loads of spell pushback you'd be better off with 2/2 imp shadow form... you make a good point that losing points in imp inner fire isn't a big deal.
Personally i'll take inner focus to macro with MB now that crit does decent damage, we only need to cast SW:P once, so this is probably the next best spell to use it on. Will probably work well with Mind Sear and it's always useful in wipe recovery to get people up quickly... for 1 point why not take it?