Doesn't change anything, in pve you are always going to use leaching because it is the only one that has any effect on anything in a pve enviroment. Everything else applies to the boss and will be immune.
Unless shiv is going to allow these effects to the boss it is just a PVP talent and every rogue will be deadly/leech.
Even if the effect apply to the boss they are too short for any usefulness without gimping dps.
Why would you assume all of this? We don't have access to the Mists Boss Design Crystal Ball (though I did put in a bid for it on eBay); how can any of us know what boss mechanics will face us in the next expansion? The alterations being made not just to the rogue class, but to all classes, can potentially open the door to some pretty wacky fight designs -- possibly involving, just as an example, lots of adds that different raid members will need to pick up or control depending on what abilities they bring to the table.
Who's to say you won't need to use Wound to prevent an add from healing itself for more than the damage your raid can deal to it? Who's to say we won't need to Paralytic-Shiv a mob to keep it from reaching your healer, who is specifically targeted by the design of the fight?
There are a number of raid fights within this expansion -- and many heroic dungeon boss fights as well, before many of us began to outgear the content and trivialize the mechanics -- in which our *existing* utility poisons would have been extremely useful if we felt we had any remote sense of freedom to use them without crippling (ha!) our DPS. (I actually remember, during early attempts on Ammunae in Halls of Origination, being specifically asked by my tank to use Wound Poison on one of my weapons to reduce his self-heal.) In Mists, we'll have that freedom. Heck, even if they *don't* demonstrably alter fight mechanics in the next expansion, just having that freedom will likely lead us to use these poisons in ways our one-dimensional brains can't even imagine right now, because the poor squishy things never had reason to do so.
I can't see it happening. Mainly because faction champs irritated so many people which goes against the casual thing.
Unless they make some stupid requirement for a rogue to be in the raid for a specific shiv ability. There will always be a range class with the ability to do what ever is required much faster without having to run over to the add or you will have people whining that there is an encounter that is impossible without a rogue which moves away from the non class specific mantra.
In the case that a melee dps is required to tank an add for some reason leeching will be the highest survivability anyway unless you need to kite it and hence every other range class will be better or a tank.
It is near impossible to imagine a situation where a melee class would be able to perform any role that a range can do simpler that does not involve leeching poison.
ie unless something really stupid happens and they implement another pvp encounter like faction champs again. There will be next to no reason to have anything other than DP/Leeching.
Shiv increased poison affects will be a pvp ability. Unless they add some interesting poison for pve that actually effects either dps, survivability or raid survivability with a duration long enough to mean that shiv should be included in the rotation. Leeching is the only one that I see ever being used in a raid outside stupid mechanic gimmick fights. I wish this was not the case but the simple fact of the matter is that ALL raid bosses are currently immune to all the other effects.