There's going to be a mandatory ROM lockout of non-approved (hobby) OSs on all new Windows 10 systems. NG Amigas have no chance of becoming mainstream. I'm going back to the classics using FPGA technology. Classics have a better chance by sheer virtue of having more software.
I think you mean Secure boot, this is part of the UEFI which prevents low-level malware like rootkits from interfering with the boot process.
Secure boot has been around since Windows 8, so it's not a new thing that is just Windows 10.
However it's up to the manufacturer of the motherboard (these days the main board) if this will be locked down or if they will provide a toggle. In 99% of cases there is a toggle in the BIOS to disable Secure boot. Most likely this will be the same with new hardware coming through for the Windows 10 generation of devices.
The worse case scenario if the motherboard is locked would be whom ever is working on the AmigaOS to x86 port (well it should really be x64 as x86 is 32bit and PC's these days are x64) contacts the motherborad manufacturer and Microsoft to have the kernel-mode drivers signed and then the motherboard manufacturer adds it the motherboard Secure boot database saying hey I'm not a viruii, malware or rootkit and it's sorted.
This also could be a good thing for AmigaOS, pick one or two PC motherboards and use the UEFI/Secure boot to look the OS to those.
This would create a stable platform and people could concentrate on developing drivers for it making it easier for developers.
Hardware would be cheaper than PPC and you would still have the predictability of what hardware is expected. A lot like a gaming console.
Oh and to add Microsoft already support Ubuntu and Fedora with Secure boot so it wouldn't be a stretch for AmigaOS. The FUD people are spreading stating Microsoft are locking out other OS's is crazy. It is to stop viruii, malware or rootkits and again 99% of the time it can be disabled in the BIOS.
It's also up to the manufacturer of the motherboard in question if it is to be compulsory or what OS's are to be in the Secure boot database on the motherboard not Microsoft.