JSX: a way to make all the properties of value-based elements optional

It's not documented, but currently, if the JSX.ElementAttributesProperty interface is declared empty,

declare namespace JSX { interface ElementAttributesProperty {} }

then the element attributes type becomes same as the element instance type. However, if the element instance type is a class, this leads to a situation where the compiler requires that all the members of the class be represented as attributes since they're not optional (and even cannot be marked as such as the class syntax doesn't allow optional members).

class MyComponent {
  myProp: string;
  private myMethod(): void;
}
var a = <MyComponent myProp='value'/>;
// error: Property 'myMethod' is missing in type MyComponent

This prevents me from using JSX for type-checking Angular 1 templates (you can find my experiments in this area here).

What if we introduce some way to tell the compiler that not all the properties are required, but only some of them? E.g. those having a certain decorator?

A related issue: #5151

The issue names no file, test, or compiler entry point. Begin by locating the JSX ElementAttributesProperty handling and related issue #5151, then review existing JSX type-checking tests; completion would require an agreed mechanism for making selected value-based element properties optional and tests covering the class example.