That's not true. If distros package closed source firmware updates the manufacturer has the ability to provide updates to people's computer via that system. I mean, that's the whole point and in a trustworthy environment that's a good thing. Maybe have a look at
https://wiki.debian.org/Microcode#CPU_microcode_non-freeness (I'm not sure whether I'm just misinterpreting your comment or whether there is a knowledge gap, just to make sure we talk about the same thing :) ).
> By withholding that information they are effectively eliminating the choice, and restricting users' freedom.
You are mixing up agency and software freedom, it's clear that you won't see eye to eye with the FSF as long as you do so.
I'm not even vigorously defending not showing the note about existing firmware updates, if Guix really does so. I'd prefer a note. Just what it would mean and how problematic closed firmware would be seemed like it needed a clarification here.