I think that's not quite right. Packs need to be able to contain tuples as elements, and so you can have packs that contains nothing but a single tuple as an element, and operating on that in a variadic-generic context is semantically different from operating on the underlying element that's a tuple. The result is that, if we're not going to introduce single-element tuples, we get this class of "things that look like tuples" in variadic generic contexts, like (T...), which is not necessarily a tuple (if T is a singleton pack of a non-tuple type) but is treated like one in the variadic-generic context. Crucially, tuple operations on such values/types have to be rewritten atomically with substitution, because they need to have the effect that they would have if single-element tuples existed and must not see through to the underlying type (which might be a tuple) if the pack happens to be singleton.
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