1. A system, comprising: a plurality of nodes coupled to a network, wherein at least a subset of the plurality of nodes are each configured to maintain a replica of a state machine; and the plurality of nodes are classified into a plurality of non-overlapping classes, and a first class of the plurality of non-overlapping classes comprises multiple nodes that are each a current participant in a consensus protocol for controlling transitions of the state machine such that respective state machine replicas maintained by at least one node in the first class and one or more nodes in a second class of the plurality of non-overlapping classes are transitioned to a state upon at least some of the multiple nodes of the first class accepting a proposal to change the state of said state machine according to the consensus protocol, the second class comprising nodes that are not current participants in the consensus protocol but which are reclassifiable into the first class; and the multiple nodes in the first class are each configured to act on the proposal for a transition of the state machine in order to collectively accept or deny that proposal according to the consensus protocol.