I remember SE saying in an interview, that when he discussed the undertaking of the Malazan Book of the Fallen with his publisher they settled on him having 10 books to tell this story. He'd need that much to tell the three big story lines he'd developed, ten books making room for a possible fourth storyline, which I think he eventually did include. I may be off on the exact details but that's the outline.
So what do you think are the main story threads and what storythreads are just subplots or perhaps just useless filler that looks like a storyline?
My guess would be:
A) The CG problem (obviously)
Subplots being:
The Pantheon War
The Master of the Deck
Kru'lls warrens and the Starvald Demelain question
The Holds vs. The Houses
Brood and his Hammer

Subplots being:
The whole Andi, Liosan, Edur history
The Deragoth and and the Hounds of Shadow
Kellanved and Dancers schemes within schemes
Then I get confused
perhaps C) is The Malazan Empire:
Subplots being:
The fait of the Malazan armies
The fait of the Malazan empire (Laseen vs. Rel)
or perhaps the entire Edur/Lether storyline was C).
Subplots being:
Rhulad, Trull and the rest of the Sengar family
The Edur vs. Human Civilization
The tyranny of money
Or maybe it's Crokus and the future of Darujistan:
From thief to assassin to hero of Darujistan
The Seguleh and the Torruld.
Then there's Icarium, his machines and the Nameless Ones (this actually seems like a big deal)
There's the KCCM, fall and return.
Envy, Spite and Draconus (and Rakes role in all this)
Dragnipur and its sundering
The Donkeygoth
The Imass, T'lan Imass, then Imass again.
The Wolves of Winter
Karsa and his future return to rule all Giant Races
The Assassins sleeping in the Azaths (STs game)
Felisin(s) and 7C --- was this a big storyline? it seems to have dragged on from DG to BH?
Dessimbelackis and TC