As of today, the rust-lang GitHub organization has been upgraded to support 15 concurrent jobs on Travis CI. Previously, it had the default for open source projects of 4, so hopefully this will help with early PR testing and usage of services such as https://nightli.es!
It should only be for the rust-lang organization. Travis billing is currently on a per-organization basis; if more concurrent builds are needed for those, we could certainly add them, but it’d be extra $$$$.