Hmm. Guaranteeing that this is an array — and therefore also the count and order of the array elements — really ties this to the details of Swift's ABI. It would not be implementable to create one of these from generic code under a different ABI, and that seems like a line we shouldn't cross. Do you think it's especially important to expose this as an array (e.g. to allow the efficient creation of BigInts from a StaticBigInt), or can we reasonably abstract access in some way?