If you look at a simC profile of affliction at the "time spent" column you see that aff spends far too much of its time channeling either DS or MG which "feel" essentially the same. Yes some fights you do a bunch of soulswapping or whatnot but when aff is played in its basic fashion the ratio of filler:dot maintenance is too high on filler. I'm kind of just going on the notion snapshotting is gone and pandemic is going out for all dot centric specs/classes.
As for drain soul in PVP how often do you *really* get to channel a shadow spell for long enough to get shards? Every stream, tourney, etc I watch combined with my own more modest experience is that you hardly get to cast period. The inability to cast issue seems to also get worse the lower down in MMR you go thus by the time you are in the 1500-1800MMR that most people pvp in you not only are less skilled than the tourney folk/have less peels but lower MMR brackets are chok full of cleaves that can make for a near 0 casting environment. 4 seconds of casting on a single spell school spec just isn't going to happen for 99.9% of the population. At all MMR's aff really lacks finishing power in pvp and a potent instant dot (as described in my earlier post) would do that.
I am okay with snapshotting going away though I think blizz needs to not fall into the trinket trap again. Their goal should be more passive gains with weaker procs since cooldown stacking is what made some specs get really out of control this expansion. Lightweave or engineering are procs but they are fractional to what you get from a trinket now. Maybe as a last hurrah final tier thing they can get back go over the top trinket procs but for now they probably need to do future trinkets closer to illustration of the dragonsoul than BBoY.
As for the mobile casting angle I think that can't be answered in the vacuum of just warlock spec balance. Its entirely dependent on what melee is getting for their "niche" and especially what other ranged are getting. Since it appears hunters, ele, and mages are still going to keep their mobile dps intact (if not expanded) for WoD I can't see KJC being toned down. I could see KJC going to a passive free filler with a on use that works on all spells.
Right now demo has multiple ways to spend its DF/spells...soulfire makes the spec interesting since you can use it to either build DF or spend it vs ToC. Aff needs something similar to give it choices to make that are situational. I think shorter duration dots, making DS an execute dot, and tighter shard regen bad RNG protection are a good way to start. If the different buttons you press to dps feel more different then the effect is you are less bored hopefully.