1 & 2. Say a government bought a sizeable amount of DRK and opened a lot of MasterNodes. What stops them from tracking at least a potion of the transactions that are supposed to be anonymous? CloakCoin's main feature (expected in the next couple of days) is called Proof of Stake Anonymous (PoSA), and it uses the PoS feature to conduct anonymous transactions. Pretty cool stuff and no MasterNodes required. Glad to hear DRK is taking steps to alleviate the potential risk here though.
3. I can see where you're coming from, but it also lowers the upkeep of the network significantly. What happens if somehow everybody stops mining DRK all at once? Not saying it's going to happen, just a thought though. PoS obviously has some weaknesses too. The main one to me is that you can just open your wallet once in awhile and get full stake without really securing that network much. This is what also got me looking at BlackCoin and its upcoming PoS 2.0 as they're calling it. A major change there is that wallets must be open to stake.
Nice to have a good discussion here once in awhile haha
1 & 2. They would have to buy an extraordinary amount of DRK considering there are already 600 masternodes. Furthermore, with IP obfuscation and I2P, they wouldn't know who the user was. If they bought 50% of the network they'd be selected 25% of the time as both masternodes. To mitigate this, a potential solution would be to DarkSend multiple times to yourself before sending to the recipient.
I'll look into the PoSA.
3. To each their own. Your scenario is not feasible, even if all the pools were taken down.