I'm in the same boat, traffic dropped 50% in a few days, 100,000's of long tail k/w.
More content being found? More competition? Might be, might not be. To have all 100k of my k/w drop positions due to competition. Hmmm.
New weighting of internal links, possible. But then everyone would be affected in the long tail field, thus canceling it out overall.
Could be Google is now crawling deeper so found many new links, that might be throwing everything out of whack.
Could be Site Speed was just introduced on more than a "test" basis.
Could be lots of things. IMO best to wait for the dust to settle.