What you seem to be doing is trying to get the "best of both hybrid builds" - the classic hybrid builds being SM/Ruin and MD/Ruin. The problem with this split approach is that you get the "best" of neither.
All this fancy stuff about sac'ing the VW and popping another will become complex and won't pay off like you're hoping in BGs. Duels? Maybe. Occasional world pvp/ganks? Maybe. But BGs and steady pvp? I doubt it.
A 2855 damage shield is good. But you can't maintain it long. And at higher levels it can go poof in a second or less. To maintain it you're summonging demons and saccing more than you are casting dots, fearing and shadowbolting (I'm exaggerating, but in my experience I can only sac so much in a bg - I run out of shards, for one thing).
What I'm getting at is that maybe if your defensive strategy eats too much of your casting/fighting time, you're spending too much defending and not enough attacking. I suppose w/ great care you could balance this, but consider just going all out in one of the "new" hybrids.
It seems the new hybrid builds are DP/Ruin (dark pact/ruin, or one of the other very high lvl affliction talents + ruin) -- and SL/Ruin (soul link/ruin -- can have other high lvl demon talents, too, but SL is the Cadillac talent in this case).
If you want "true" defense, get MD. Sac a VW, pop a new one - and now you have a damage shield AND -10% to damage from md/vw combo AND -20% to damage from Soul Link. You can get DK (and consider going even harding into Demon for DT and get +5 to crit, which is really NICe - and perhaps you SHOULD, as most locks say Ruin only really shines w/ at least a 20% or even 25% crit rate (aim for 25%, I think most say that's the point where, in terms of raw #'s, ruin shines).
See what I'm getting at? You lose Nightfall, Fel Conce and some other nice mid-lvl Affl talents, but you gain some of the BEST demon talents (MD, Soul Link, DT). Just go 5/5 in imp cor - maybe improve tap. Imho a 7/33/21 (I think this goes up to SL and 2/3 DK) or a 5/35/21 (gets SL and 3/3 DK) or -- give up imp cor -- and get SL, DK and DT -- 0/40/21 build.
OR...
Give up demon and go heavy Affliction. Top end Affliction, Dark Pact, instant HoT (howl o' terror), Curse of Exhaustion -- CoEx can be used to kite, thus mitigating your glass cannon status somewhat like a frost mage does. SM is good, and SP also mitigates being "glass" by draining target to heal you (mult-cast this if possible).
The SM/Ruin or DP/ruin build, whichever we call it, can still go 5/5 in Demonic Embrace for some nice extra HP's. And you can just get some green "of stamina" outland gear to boost your hp's a lot - it's crazy what it can do.
In other words, don't water down your build to lose your glass status -- water down your mana pool and some of your +damage gear. Mix and match, green "of sta" gear from outlands is usually cheap on the AH.
Anyway, these are just options. Imho you will hate a 20/20/21 build (or whatever combo you had) - your affl and demo talents, doing that, are just too weak to be any good - again imho. And you have other options.
If you want ruin + demo's defense, by all means consider the SL/ruin build. Mid level affliction talents do nothing compared to the high demon talents. You won't get Felg and Ruin in same build, of course, but the other top demon talents are really nice. Nightfall imo isn't worth it. Procs too infrequently to give up the high end demon stuff. Or go DP/ruin and get gear and dem emb to get HPs. Play around with this before locking in. GL!