I haven't played Wotlk yet, but I assume Warlocks > Ele Shamans in dps. Warlocks being a dps only class and all.
ToW is about twice as good as Demonic Pact. (the gap lessens as my warlocks gear becomes better, but I don't really expect to hit over 2800 spell damage)
The "extra" bloodlust is negated by the debuff. I'm not expecting mana troubles, so mana/healing stream doesn't hold that much value.

So I would be losing personal dps, a potential OT (voidwalker), a potential HP buff (imp), summons, and the best aoe in the game.
And gaining 140 (or less) spell power for my group, a shorter CD on wipes (reinc vs SS), and resist totems.
Min-maxing. Yes, an ele shaman would probably net a higher DPS for the group, but I personally believe the warlock offers more utility than a second shaman due to the OT if needed. Summons are also a very nice thing to have.
I'm sure your opinion will remain different than mine, but you asked why I was "even considering" a warlock, and there is my reply.

On another note, I am thinking about using the FTL PvE Lock and Hold control system. Not exactly targetless, but I don't think the mobs can use who I am targeting to their advantage :) Every normal spell has /click <target and hold assister> Every counterspell key clicks one without /stopmacro in it (so that it always assists)

Target and Hold Assister
/stopmacro [exists, harm, nodead]
/assist [mod:lctrl,nomod:ralt,target=Toon1][mod:lctrl,mod:ralt,target=Toon2][mod:rctrl,nomod:ralt,target=Toon3][mod:rctrl,mod:ralt,target=Toon4][nomod:rctrl,mod:ralt,target=Toon5]

Then I'll have F bound to /cleartarget on everything except my main so that I can change targets easily if needed.

I can't think of a good way to do CC though.
Maybe something along the lines of:

/assist [mod:lctrl,nomod:ralt,target=Toon1][mod:lctrl,mod:ralt,target=Toon2][mod:rctrl,nomod:ralt,target=Toon3][mod:rctrl,mod:ralt,target=Toon4][nomod:rctrl,mod:ralt,target=Toon5]
/clearfocus [modifier:shift][target=focus,dead][target=focus,noexists]
/focus [target=focus,noexists]
/cast [target=focus] Polymorph
/targetlasttarget

The problem I forsee with that is: pressing it while targeting <TGT> but wanting to sheep <FOCUS>. The macro would sheep <FOCUS> correctly but then it would /targetlasttarget, and <FOCUS> would become targeted by the mage. (or whatever it had targeted before <TGT>) At which point the next damage spell would hit the sheep.