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from a blockchain perspective, it should scale and the witnesses will be able to add further capabilities. From a speammer/Id thief perspective, it is about educating those who are here for benevolent reasons. if it happened today, it would struggle, if it grows slowly, there are definitely ways to combat it as the steem decentralises giving more weight to more people. The team will of course grow as required also.

Only time will tell. But am loving Steemit for sure.