I agree that the shipping dates would have been tight, but given Apple's relationship with AMD (like getting certain Navi cards in the MacBook Pro months before

I agree that the shipping dates would have been tight, but given Apple's relationship with AMD (like getting certain Navi cards in the MacBook Pro months before they shipped anywhere else) I think they could have pulled it off. The Mac Pro is also a relatively low volume device, so AMD could have done an early run just for Apple like they have done with other HPC customers. Both Apple and AMD have enough clout with TSMC that they most certainly could have made it happen. Apple could have been well aware that AMD had a winner in the works, years before launch. I feel like Apple could have easily prototyped the Mac Pro on older TR designs and evolved the design as AMD got deeper into sampling the current gen. I think what eliminated the risk of switching to AMD for them was the ability to test their thermal design on already shipping parts from Intel. The chipsets haven't changed at all so they've been working on a stable platform since day 0. Or maybe they got an offer they couldn't refuse from Intel. CPU compatibility with macOS is also a total non-issue, considering how well the AMDOSX community is doing.