Almost all of those don't work/help. Please recall that most of those abilities can be targeted at melee, so if there's no legal targets at range (due to Smoke Bomb or whatever) they can still do it on melee. So:
Marrowgar: You could probably make him always spike melee... ok, who cares. You can achieve the same effect by just having everyone stand in melee range anyway.
LDW: I suspect you just wind up with them all running into melee and then casting it. Which again, doesn't help that much.
Saurfang: He always marks melee. Might make shaman healing it a little easier, but hardly game-breaking. Unless you're advocating having all the melee stop DPS and run out to a cloud, which is bad for other reasons. And somehow I suspect piling multiple marks onto the tanks would be an extremely bad idea, particularly in hard mode, anyway.
Princes: Empowered Vortex is not targeted but AoE, so would be unaffected. And if your ranged are struggling with Empowered Vortex, you have other issues.
Did you even read what I typed?
Marrowgar: He *can not* spike tanks, thus the cloud prevents all spikes, not just confines them to melee.
LDW: The adds are not the ones casting the MC, LDW herself is, and as far as I know she can't move during P1, thus potentially no MC is cast at all.
Saurfang: No, he does not always mark melee. He marks a random raid member, tanks included, and by putting your whole raid (other than tanks) under smoke, you force the mark to get put on a tank, which is a pretty big advantage for any guild still struggling with normal mode or working on hard mode.
Princes: The effect that the empowered vortex produces is an aoe effect, but the application of each "debuff" so to say on each player which produces the aoe effect is a single target ability. That's like saying mages will be able to living bomb a rogue under smoke, I highly doubt this. Just like empowered vortex, LB is a single target spell which eventually produces an aoe effect.
I don't mean to pick nits over somewhat tiny perks, but you seemed to have misunderstood every single bullet on the list, and I agree, these aren't huge perks to any guild that farms normal modes, but I'm more thinking of guilds on working on hard modes or guilds struggling on normals. Likewise, my original intent was not to entail all of the overpowered applications, I was just giving a brief list (emphasis on brief, many more applications exist) of why I believe boss abilities are going to ignore this mechanic entirely.