These are good examples. I think they highlight the need for this rfc process to stay very lightweight, and mainly focused on raising awareness of things that are happening across the projects. I’m pretty sure that none of these things would have happened if there had been a prolonged, concern-heavy discussion of all the eventualities and unlikely failures before any code was written.
And yes, 'informal RFC" is a good way to describe the preliminaries that lead to these initiatives happening. I did talk to the designers at various points about using fonts for symbolic icons, and even wrote prototype code for that approach (there was no interest, so I dropped it). The work on the new symbolic parser(s) in GTK over the past year was done in cooperation with Jakub, so the design team was involved and had a large influence on the direction. But: we could not have written a roadmap for this feature 2 years ago. It would have been totally wrong