Well, the latency is far from negligible. However, the bandwidth really is impressive. Having userspace as the control plane while keeping the data plane firmly in the kernel has long been the way of things, and this blog post's not-so-subtle message is "your problem is not novel enough to justify the cost of your solution".

To be clear, there is nothing fundamental (to the best of my knowledge) that would prevent Weave implementing a VXLAN backend. It is simply a poor implementation at the moment, and even then, only in this regard. Who knows, maybe Weave's use of a gossip protocol vs flannel's CP etcd could make it more suited to some deployments. Though, that does need to be tested.