This machine is way out of my price range; but I am very interested in the frequently mentioned "open-toolchain FPGAs" in their descriptions.

AFAIK there are only a handful of very specific chips that you can currently get away with not using vendor tools against, like ICE40s.

I would be willing to put a fair amount of money into crowdfunding for better open source -full- toolchains for FPGAs (especially something targeting Xilinx devices). The vendor tools, aside from being closed source, are all huge bloated disasterpieces, and none available for macOS.