Why the limitation on exporting an interface by default in TypeScript?

Question

I'm using TypeScript 1.5 beta, and I'm trying to export an interface as the default export. The following code causes an error in both Visual Studio and WebStorm:

export default interface Foo {...}

However, the following code works fine:

interface Foo {...}
export default Foo;

Is this by design, is it a bug, or am I doing something wrong?

EDIT: Thank you for your answer. It begs the question, however, so what is the accepted way to import an interface using the ES6 module syntax?

This works:

// Foo.ts
export interface Foo {}

// Bar.ts
import {Foo} from 'Foo'; // Notice the curly braces

class Bar {
    constructor(foo:Foo) {}
}

But, since that works, why not allow a default export and save the curly braces?

// Foo.ts
export default interface Foo {}

// Bar.ts
import Foo from 'Foo'; // Notice, no curly braces!

class Bar {
    constructor(foo:Foo) {}
}

Solution

TypeScript v2.4.0 allows export default interface. Here is the pull-request that introduced the change.

We can now do both of these:

// Foo.ts
export interface Foo { }

// Bar.ts
export default interface Bar { }    

// Baz.ts
import { Foo } from "./foo";
import Bar from "./bar";

export class Baz implements Foo, Bar 
{

}