The krpc subsystem ensures that only one connection exists between any pair of nodes, but it doesn't coalesce the RPCs themselves. In clusters with dense nodes (especially with a lot of tablets), there's often a great number of RPCs sent between pairs of nodes.
We should explore ways of coalescing those RPCs. I don't know whether that would happen within the krpc system itself (i.e. in a payload-agnostic way), or whether we'd only coalesce RPCs known to be "hot" (like UpdateConsensus).