I was actually thinking about some similar changes the other day and i like most of your ideas. Here's some other ideas that i'm just throwing out there. Some are really wild and probably unrealistic but it's all under the assumption that we'll have the kind of big makeover op is talking about:
Overall: Combo points as a player buff. I know gc has commented on it but it simply makes more sense.
Assa:
-Spec idea: Burst damage and steady poison dps and debuffs.
-No more Snd/rupture rotation
-Bring back cold blood in some form! Perhaps a new kind of finishing move or a cd with charges or something. I don't care, i just want it back.
-Both lethal and nonlethal poisons unique to assa. Maybe even make poisons active abilities? Either in some kind of combination with shiv or by themselves. For example if there's a caster add in a raid you could just mind numb him directly without applying the poison first. Or use it to build up deadly stacks in your rotation. No more autoattacks proccing poisons. Would give more flexibility and give the spec a better debuffing niche.
-This could give envenom a more distinct role as the "instant poison proccer".
-Dispatch, vendetta, and venomous wounds needs to be changed, but i'm not sure how yet.
-New abilities, like the poison aoe op was talking about (instead of FoK which should be more of a combat spell).
Combat:
-Spec idea: Physical steady dps, keeping up important buffs, actively reducing cds on AR and SB and active deflection/mitigation.
-Killing spree: Remove cooldown and make it drain energy. That way it's good burst damage but can hurt your long term dps since it doesnt generate cps. Feels more logical to get tired instead of energized after the ability aswell.
-Snd unique to the spec. Maybe make the duration alot shorter so it's actually a challenge to maintain? Like 10-15 sec duration? Double attacks instead of haste like the op is suggesting is interesting, and there could be other ways too.
-More distinct defensive abilities, both active and passive.
-No more poisons/rupture.
-Restless blades is one of the coolest new things about combat imo. Could be buffed and tied to recuperate instead of current mechanics though. First of all it makes sense to get some adrenaline back after recuperating. Second it gives the combat rotation some "passive" selfhealing and third it would only be useful when the fight lasts longer than the cooldowns, ie raid bosses.
-Change revealing strike to something remotely interesting.
Sub:
-Spec idea: Stealth, illusion, bleeds and traps.
-Give sub a couple of traps. Alot of unexplored opportunities here.
-No more Snd/poisons.
-Rupture would need to be changed into something interesting if it's gonna be more of a core spell for sub.
-New sub cleave: Creates a shadow copy of yourself that follows a different target and performs the same spells you do. Combination of old blade flurry and DKs dancing rune weapon.
-Distract also applies the find weakness debuff.
In general i've always felt that the concepts of assa/sub has been very similar and another idea would be to merge the two into one spec and introducing a new third spec instead. The same is true for hunters with MM/survival i think. Hopefully blizzard won't introduce another new class in WoD so that would give them the opportunity to rework several of the existing classes instead.