Hello?
Miners in the form of big pools are several orders of magnitude more of a threat than Masternodes in the hands of a few, because Masternodes are chosen randomly each block from the whole set. Go do the math, or read any one of my many posts explaining it.
edit: If a random subset of miners were chosen each block too, that would do away with the mining centralisation issue... but so would making p2pool mandatory, or integrating pools and Masternodes... but nobody seems very interested apparently in addressing the great big fucking liability that mining in its current form presents.
Masternodes: Chances of successful attack = (rogue nodes/total nodes)^number of masternodes involved, eg if a transaction goes through 8 random nodes, and 51% of the network is compromised, chances of successful attack = 0.457%
Miners: Chances of successful attack = 100% if one bloc controls >50% of network. Currently 3 pools control > 52%.
0.457% vs. 100%
Yeah, it isn't a strictly apples to apples comparison, but you get the gist.
Icebucket's concerns are pointed in the wrong direction.