The Io XT does work on windows but yes, most AJA marketing is geared towards Mac. That is because many of their devices are centered around ProRes and Mac users. Don't forgot that AJA really got big as hardware for use with Final Cut Pro (legacy).
Unfortunately though there is no way to connect an Io XT to a computer without Thunderbolt connection. The Apple adapter that you speak of is not simply a cable adapter and it requires the thunderbolt controller inside the computer to interpret the ethernet signal. An interesting thought for sure, though I would suggest that you look towards other options.
What is the computer that you are trying to run? A PC laptop or desktop? If it is a desktop you can always get a Kona desktop card and when you upgrade to a machine with thunderbolt you can put in a thunderbolt PCIe chassis such as those available from Sonnet, Magma, or OWC. This will give you the flexibility to connect it to a laptop later and it will really be no different than an Io XT which is really a Kona3G card in an external thunderbolt chassis combined with pieces of the Kona breakout box.
Co-President at fourB Productions, Inc.
Blackmagic Cinema Camera, RED Scarlet-X
2011 Macbook Pro 17", 2.3 Ghz Quad Core, 16GB RAM
2008 Mac Pro 2.6 Ghz 8 Core, 10GB RAM
AJA IoXT, Blackmagic Intensity Pro, Blackmagic Mini Monitor
Adobe Production Premium CC, Avid Media Composer 7, Final Cut Pro Studio 3