That is something that no one outside of Apple can say for certain. It doesn't even have to be a major change, but something like rearranging ports, adjusting taper or extrusions on the chassis, etc. Those kinds of adjustments happen all the time on consumer hardware, and most people don't notice, but may be an issue if you're trying to fit into precision machined slots.
> Hardware will almost always cost less than engineers.
For commodity, off-the-shelf hardware, absolutely. This is anything but, and still requires engineering effort to design, fabricate and assemble. And it's not always about the immediate dollars: sometimes a fundamental reworking means sacrificing short-term savings in favor of the long-term: flexibility, risk mitigation, reduced operational complexity, and cost over successive generations of hardware.
