You can install Node Nightlies/RCs via nvm using NVM_NODEJS_ORG_MIRROR environment variable.
Install latest Node RC
NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/rc/ nvm i nodeInstall latest Node.js Nightly
NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/nightly/ nvm i nodeInstall latest Node ChakraCore
NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/chakracore-nightly/ nvm i nodeInstall latest Node v8 Canary
NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/v8-canary/ nvm i node