Based on the subsequent research I did on the topic since posting the question, and then having that research confirmed for me by magicandre1981's answer, the answer to this question is currently...
Yes, but only if you have an Android device with an x86-based processor
This excellent YouTube tutorial here proves that much by outlining the process of installing Windows 10 on an x86-based Android tablet, and for what it's worth, the installation looks like pretty standard stuff. In that tutorial, he installs the Windows 10 Technical Preview, but on further questioning, he insists that it's possible to get any version of Windows 8 or 10 onto it.
So ultimately, it comes down to whether your Android device's processor architecture is x86-based, which can be checked. I'm not personally sure how common x86-based Android devices are, but it's a good start, I suppose. Now I just need to check whether my mate's tablet is x86-based or not.
And like magicandre1981 pointed out with the MS press release from just a few days ago, in the future we can hopefully look forward to all ARM devices supporting Windows apps natively.