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The Steemit Inc. ninja-mined stake consists of approximately 74M STEEM tokens, some liquid and most powered up in @steem, @steemit, and @misterdelegation.

At the current rate of ~509.95 STEEM per MVEST, that is approximately 145.1 gigaVEST of witness voting power. If you look at the current list of witnesses, you will see the top witness has about 89 GV of approval. If used, the Steemit Inc. ninja-mined stake can put the top witness into the 31st position.

if the approval rate is the only thing you're measuring, then I have to say the non-voting stake would mean they are not approving the current witnesses. as long as Steemit does not hold the absolute majority of supply, I see zero reason to do anything.

This is more and more becoming the EOS route, only a matter of time until cartels build. If Sun doesn't fork, that is.

Majority or minority of stake isn't a relevant point.

Can a single entity control the blockchain consensus? The answer is (was) a clear and present yes.

Should the blockchain witnesses have done something about this before? Yes, but the can was kicked down the road because the incentive structure for the owner of that stake and their promises were enough to not establish a consensus. The new owner does not have those incentives and did not make those promises. Furthermore they have communicated an intention to deprecate Steem.

Is that all of it, or is there millions more in sock puppets so that it will be a long time before ned stops profiting from selling steem?

When does the community stop voting rewards to weak hands?
Seems we got to do that, if we want the price to rise.

They own about 30%+ of the vested steem and ~20% of the supply. In theory not enough for unilateral control but more than enough in practice due to voter apathy. I think that Vitalik Buterin was the first to point out this weakness of DPOS.