One of the reasons this is so relatively simple is that it doesn't appear to handle cycles like es6-module-transpiler does.
See the test case here:
https://github.com/thomasboyt/es6-cycles-comparison
The es6-module-transpiler output functions correctly, while the Esperanto output does not. This means that while Esperanto can translate the syntax of ES6 modules for you, it doesn't currently match semantics like es6-module-transpiler does.