Right now in the runtimes when a native exception is thrown which you catch with a try/catch it is the native exception object that you get.
So in my apps/N fork i use something like this:

export function wrapNativeException<T = any>(ex: NSError, wrapError: (...args) => T = (msg) => new Error(msg) as any) {
	if (!ex) {
		return;
	}
	if (typeof ex === 'string') {
		return wrapError(ex);
	}
	if (!(ex instanceof Error)) {
		const err = wrapError(ex.toString());
		err['nativeException'] = ex;
		//@ts-ignore
		err['stackTrace'] = com.tns.NativeScriptException.getStackTraceAsString(ex);
		return err;
	}
	return ex;
}

That method wraps the native exception in a JS error with stackTrace.

Would be pretty awesome to have that done automatically so that the error object you get in catch is an actual JS Error.
I think for now if we can do it it should be optional and disabled by default