> The cables and cards for PC Thunderbolt retrofit are far (like 3-5X!) more expensive than the MLNX cards and optical cables.
I added new Thunderbolt3 PCIe cards (Gigabyte Titan Ridge) to two of my 2012 Mac Pros for around $100 each a bit over a year ago and the prices have dropped since, so I don't get how that is 3-5x more expensive than MLNX cards. Expense was way way lower a factor than the finesse it took to get MacOS to support them for me, but it was the only path that worked for my needs (different need than OP article) and so I endured the pain of getting it working.
I added new Thunderbolt3 PCIe cards (Gigabyte Titan Ridge) to two of my 2012 Mac Pros for around $100 each a bit over a year ago and the prices have dropped since, so I don't get how that is 3-5x more expensive than MLNX cards. Expense was way way lower a factor than the finesse it took to get MacOS to support them for me, but it was the only path that worked for my needs (different need than OP article) and so I endured the pain of getting it working.