A while ago I downloaded the pre-release evaluation version of Windows 10 (32-bit version) to take a look at it. I installed in a virtual pc on my spare desktop and checked out its features (pretty much like Windows 8 with a built-in "Start" button on the desktop). Then I read an account on another forum where somebody said that it seemed to run well on older, low-spec hardware. So...I dug out my Mini 9 and a spare KingSpec 16GB SSD
that I had for it. I burned the Win 10 iso onto a CD and installed it on the Mini 9 using an external USB CD/DVD drive.
The installation went surprisingly smoothly and most hardware was recognised and appropriate drivers installed. I had to install the WWAN driver separately (haven't tried using the WWAN function yet). The ony other real hassle was the screen resolution as Win 10's metro interface is like Win 8 and won't work with the Mini 9's 1024x600 screen resolution. However, that was fixed with a hack (all Display1_DownScalingSupported registry entries set to 1 using Regedit). I still have a couple of "base sytem devices" showing as not having drivers in Device Manager but I think these are related to battery switch functions and not of crucial importance.
The Mini 9 boots to the Win 10 login prompt in around 30 secs and to desktop in about 1 min 20 secs. It seems reasonable quick when running applications. LibreOffice Writer loads in 41 secs and then seems to run OK with no lagging of keystrokes. The PaleMoon browser (a lightweight Firefox-derived browser) opens in 21 secs and then seems quite snappy in operation.
It seems to me that Win 10 stands a chance of allowing people to bring their old Mini 9's back into useful Windows OS service (if the cost isn't prohibitive and they don't mess it up prior to release).
One minor gripe - the Windows Defender keeps giving false positives about a "VirusDOS/Dexo". When I first saw it I was alarmed but a quick bit of research showed that this is a quite common false positive on Dell pcs.
Update - the "base system" devices turned out to be JMicron
PCIe SD/MMC Host Controllers. The SD slot was working fine on the generic MS driver but I downloaded some Win 7 32-bit JMicron drivers from the Lenovo site anyway and they installed fine.