The notion of cached compilation or remote cache has been around for a while now, but often it required the setup has not been easy. If we can bake build-as-function feature into basic tool chain such as Zinc and sbt, Scala community in general can benefit from it to speed up the build.
Even for open source projects, if Travis CI publishes into Bintray or something, the contributors might be able to resume compilation off of the last build.
The PR for sbt change is sbt/sbt#5534, and the virtualization change in Zinc is sbt/zinc#712.