New behavior

No property existence check for object type.

let foo: object;
foo.bar; // no error

Rationale

The current object type is useful when used to type function arguments but not very useful on object members. See this IDL:

[SecureContext]
interface PaymentResponse {
    [Default] object        toJSON();

    readonly attribute DOMString       requestId;
    readonly attribute DOMString       methodName;
    readonly attribute object          details;
    readonly attribute PaymentAddress? shippingAddress;
    readonly attribute DOMString?      shippingOption;
    readonly attribute DOMString?      payerName;
    readonly attribute DOMString?      payerEmail;
    readonly attribute DOMString?      payerPhone;

    Promise<void> complete(optional PaymentComplete result = "unknown");
};

Here, the details member can be any "object" depending on payment method behavior. Current lib.d.ts defines this member as any so that a user can access any untyped members.

let response: PaymentResponse;
let { details } = response;
details.anImplementationDependentMemberName; // great

But any means it can be boolean, number, string or even null or undefined.

if (typeof details === "number") {
  // `details` is resolved as `number` but really should be `never` here
}
details++; // no error, :(

A language service should be able to warn on these cases while still allowing arbitrary member accesses. Allowing such free accesses on object type will help here:

details.anImplementationDependentMemberName; // still great
if (typeof details === "number") {
  // it cannot be a number, so `never` here
}
details++; // error now :D

Hey, a function can also be an object in TS!

Yes, but I don't think the fact will cause any problem as functions can also have arbitrary members. And I'm not proposing arbitrary function call.