Note: In the months since this post, an official update has now been issued through Windows Update, and would have reached any device with this card in the Anniversary Update, if not before.
After upgrading my wife's older Dell laptop from Win7 to WinX with no problems, I was rather taken aback that my Toshiba Satellite Pro L770 (bought just before Win8 released, to tide me over until the next version after) failed some time around the 80% mark, and rolled back. And more so when the Toshiba site indicated that my laptop was not supported for upgrade, even if the Microsoft scan gave the all OK.
Cutting a long story short, it turns out that it's the WiFi card (Qualcomm Atheros AR9002wb-1ng) which doesn't have a suitably modern driver. Disabling this from the device manager before trying again let the upgrade go through, and a generic WiFi-n low-profile dongle from Maplin which I had to hand "just worked" when I plugged it into a USB socket.
Don't re-enable the Atheros card, as that gets you into a blue-screen/re-boot loop until you can get into safe mode without networking to disable it again.
Later (12-Sep): Uninstalling the Realtek PCIe GBE Family Controller device, then scanning for hardware changes and re-installing it with the latest driver already on the machine (version 9.1.401.2015 dated 4/1/2015) also deleted and reinstalled the Atheros card, leaving it enabled and not crashing the machine (while still using the dongle for WiFi).
Trying to disable or uninstall the Atheros card at this point caused me blue-screens with the same thread exception as before; but at least not immediately on start-up, so I was able to shift-Restart into safe mode, and uninstall it there. On restarting, the "new" hardware was detected, and the old 9.x.x.x driver dated some time in 2010 which previously had been claimed to be the most recent version was replaced by version 10.0.0.270, dated 10/17/2013. This was not such an improvement -- it blue-screened in familiar style when trying to disable the device.
So, once more into safe mode to disable it again, until such a time as a real WinX driver appears, if ever. Yes there is a 10.0.0.308 mentioned on the unofficial Czech site, but the summary list doesn't show any WinX support, so I'm skeptical about it (especially as the device manager update function claims that I already have the latest version).