Since there are features in Io that are neither in the current version nor planned for the future versions of Node, I guess Io.js should be explicitly specified

Since there are features in Io that are neither in the current version nor planned for the future versions of Node, I guess Io.js should be explicitly specified as an engine in the package.json file of Io-specific modules. Tracking those modules will be a good metric of how well Io is received by the community.