Like you I've installed Windows 10 technical preview on a laptop
It worked, with the added bonus that Win 10 actually fixed the borked Win 8 OEM installation in the first place.
I didn't know what the problem was with Win 8, I spent a little time trying to fix it, then went and bought my wife another cheap laptop.
I've been tinkering with PCs / Laptops for years, but I'm at the opposite end of the scale, a rank amateur.
I was as concerned and upset by the concept of being blocked from installing Linux as anyone here : I've dual booted every new PC / Laptop I've bought in the last 5 or 6 years.
The way to install Xubuntu was to get into Win 10 PC Settings / Update and Recovery / Advanced Startup / Use a device, and boot a USB device (in this case a USB DVD).
These settings still exist, even in Build 9926, the latest I have downloaded. (Notifications / All Settings / Update and
I don't know if this is the "shim" I've seen others here refer to, but it appears Grub takes over and is the first to boot. One of the options in it is to start the Windows boot loader.
So, even if it is mandatory, is it that big an issue? I understand many O/Ss don't have a PK, but someone has already suggested using something like a Redhat or Ubuntu kernel to get past secure boot.