Hi,
a) Future CPUs will be backward compatible and will run all OSs (that the computer's firmware supports - e.g. you're not going to be able to boot MS-DOS if the system is "UEFI only").
b) The other stuff inside the same chip as the CPU (mostly GPU) will work on any OS that provides drivers for it.
c) Microsoft have said "for newer CPUs/chips, that other stuff (mostly GPU) won't be officially supported". This doesn't mean it won't work ("unofficially supported"). Mostly it only means that device driver developers can stop providing drivers for older versions of Windows if they want to (and blame Microsoft when people complain instead of taking all the blame themselves).
d) Alternative OSs will be unaffected, and will continue to have no drivers for recently released hardware (the same as it's been for the last 20+ years).
e.1) For secure-boot, it's unlikely that (for laptop/desktop/server) computer manufacturers will remove the option for disabling secure boot (even though Windows 10's logo doesn't force them to provide it); partly because it's already in the firmware and they're not saving any $$ by bothering to remove it, and partly because it reduces the target market slightly and costs them $$ instead.
e.2) The main thing to worry about with secure-boot is something I'd call
"boiling the frog" - increase the restrictions a little ("Hey, we forced manufacturer's to provide an option to disable it!"), let people get used to it, increase the restrictions a bit more ("Hey, manufacturer's can still provide an option to disable it!"), let people get used to that, increase the restrictions a bit more...
f) Systems using other CPUs (ARM, MIPS, etc) will continue to be far worse (because there's all the same problems; but far fewer standards that an OS relies on, like PCI and firmware).
Cheers,
Brendan