So you're saying that you'd build a tuple (or some other structure) of tuples of references to construction arguments. You'd still be constructing a series of successively larger objects from smaller ones, but those objects are made up of a bunch of references, and references are trivially copyable from the implementation's perspective (though not from the standard's). So those constructions would likely be optimized away via memcpy elimination, or, even if they weren't, they'd be relatively cheap. Am I understanding correctly?

I suppose that works, as long as you can determine all the construction arguments in advance. It wouldn't work if, e.g., later elements of the tuple are constructed with pointers into earlier elements, so that you'd need the earlier elements to already be constructed before computing the construction arguments for the later elements.