Hello,

Under Windows, if you go into the Safe Mode options and select "Enable Boot Logging", after booting a file called "ntbtlog.txt" appears in the Windows directory. The file contains entries like:-
Is there a way that I can obtain a similar list of modules, firmware blobs, etc. in the order that the Linux kernel loads/reads them? (Timestamped would be even better)

I don't think so.
First of all kernel is multithreaded, the order of the drivers may depend on a lot of things.
Some of the drivers are built into the kernel, it does not need to load it.
Some of the files are not accessed directly by the kernel, but a program which was started during the boot (like init or systemd ?).
But anyway all the files (including config files) are handled by the kernel (you may check the function access or open).
What about the virtual filesystems, like /proc, /dev ?
Kernel has no any idea when the boot itself is completed.
You can check the loaded modules with lsmod.

By the way: what do you want to achieve at all?

For earlier parts of the boot process (i.e. kernel logging), see dmesg

Strictly speaking, the kernel doesn't read files - that's a user-space function. It does provide call-backs for filesystems to provide interfaces that can be called as needed. I suspect Windoze isolates functionality similarly although I haven't looked in a bunch of years.

It would pay to define what you mean by;
- kernel
- boot

User-space initiation is way after boot has completed ... there is even an argument that the kernel is not even involved in the booting process (of the hardware itself). Not necessarily just semantics either.

My intent is to determine what modules/firmware two x86 machines (one Intel, one AMD) load at boot and then trim the modloop so nothing else is included.
These machines are used for networking infrastructure, there is no expectation of connecting weird and wonderful PCI/USB devices.
I have tried manually removing files, but encountered problems (e.g. most of the AMD graphics firmware blobs are interdependent).
My definition of "boot" is "everything before init starts".
I think that Kernel Function Tracing may allow me to filter on file operations?

That is lsmod. (list modules). But probably you can build your own kernel with all your required modules (as builtins) and without any other ones. (also without module loading functionality). I don't really understand exactly what did you try?
And some modules probably loaded after init started.
yes, you can do that, just that won't help you.