I haven't done any "coinmixing work"— if you're talking about CoinJoin, darkcoin threw around my name quite liberally initially until people warned them not to. I don't want my name anywhere near this thing.

Maybe it is— how would you know?  ... in any case, randomly selecting a server is distributed but not decenteralized. The "random" servers are well positioned to track every user using them.  A well implemented coinjoin would combine users with multiple other users in a way that _no one_ knows what the input/output correspondence is beyond each user knowing his own inputs and outputs.

PS, masternode centralization in the future doesn't cause any problems for darkcoin. I have 2 possible solutions to evaluate for V2 of darksend (ring signatures and encrypted system where the users themselves do the joining relayed through the masternodes.) . Both of these make the masternodes unaware of who is sending money to whom, so centralization isn't an issue at that point.