And also, dos attack sounds highly inefficient because even if you'd get all the other nodes out, the data you're grabbing with your own nodes will mostly be uninteresting to you, and the trail will end very soon because the funds are constantly being anonymized. A script which monitors your node's status and launches a new node on a different service operator if needed could also be developed.
I don't know whether masternode owners turning against each other is plausible, as that kind of activity would affect the coin valuation negatively, so I doubt the incentive is there, but we'll see.
Well no, if you read about the 2nd part you would see that DDOS-ing 1000 MNs isn't even that hard.
Didn't say it wouldn't be hard - no idea if it is or isn't - I just said the incentive to ddos is minimal. You will ddos the whole masternode network, and after some time the wallet realizes what's up, and disables anonymization process. If someone you're interested in happened to anonymize his incoming funds in that exact time window you might get something, but what are the odds your ddos resulted in anything? Small I'd guess. Therefor, no incentive.