We tried this, you can kill the 3 pulls in the plague wing with less then 10 people. 1 person can kite the slimes. 2 priests to shackle the ghouls and 1 tank + dps on the 3rd ghoul. Worse come to worse, ghouls can be snared so you can also kite them but it's harder then slimes.
We got incredibly lucky and got 2 harbinger of doom in our first 5 trash packs kill over 2 nights. Don't expect that obviously.
Death wing trash are much tougher but I guess if you split them correctly you can tank them somehow and kill them with a small group. But I doubt 10 would do it.
It's pretty much impossible to kill the gargoyles with less then 25-30 or so so you can't go that far in the plague wing after those 3 ghouls pack.
A Warlock can solo the first pull in the Deathknight wing. Stand on the transporter, send your pet in. When the pet gets back to you, the mobs deaggro because of an oddity with how linked aggro works. At this point, you toss a DoT on one of the mobs and it splits. Curse of exhaustion + corruption and kite it around the room until dead. One of our warlocks has been doing this for about 12 hours a day for the past week or two, trying to get a Garb.
Speaking of trash drops.. Has anyone seen Life Channeling Necklace drop from trash on live servers? Neither Thottbot (live) nor Allakhazam have any info on it.
I highly doubt it actually drops from trash. wowwalkthroughs/worldofraids lists anything they don't know as trash/misc. My best guess would be saph/kel which is a shame since it isnt that much better than the C'thun neck.
Horsemen. All the "trash" drops that clearly don't drop from trash are almost assuredly from the Horsemen (bearing in mind that our enterprising hackers didn't seem to DT each of the four last to fully explore the loot tables -- they just killed Mograine last for Ashbringer). They're all about the right ilvl, too. Sapp and Kel drop ilvl90 and ilvl92 stuff, respectively, and their tables were pretty heavily explored.
Ghoul packs can be done with three priests. Just Shackle/smite kite them while dodging the slimes. It'd take a stupidly long time if you didn't have any other dpsers, but really the only way to fail would be to get bored.