I making a plugin-based system where plugin authors can provide plugin data in the form of JSON files. Justin helped me find the following solution:
npm install --save-dev system-json
then:
System.import('foo/data.txt!system-json')
The file format can be anything (including JS), and the data will be loaded as a string and parsed using JSON.parse, giving us a consumable Object.
Answer was discovered here on gitter.