What problem does this feature solve?

When an module is imported statically, dynamic imports to that module can be inlined.
For example of https://stackblitz.com/edit/rolldown-rolldown-starter-stackblitz-5krehyfj?file=src%2Fentry.js,src%2Ffoo.js , the output can be:

const foo = "foo";

var foo$1 = /*#__PURE__*/Object.freeze({
  __proto__: null,
  foo: foo,
  [Symbol.toStringTag]: 'Module'
});

console.log(foo);

Promise.resolve().then(function () { return foo$1; }).then(mod => console.log(mod.foo));

This is what rollup does (repl).

refs #4904

What does the proposed API look like?

Not an API change