There are a bunch of scale limits in Kubernetes itself that are being chipped away at; the bottleneck is not the scheduler, so plugging a new scheduler in won't make the system more performant.

Here's a blog discussing the current state of K8s scale: http://blog.kubernetes.io/2015/09/kubernetes-performance-mea...

Note that Bob Wise at Samsung has been driving some horizontal scale testing, and has got a 1000-node cluster up and running, so that's a current "best case" scale number.