This whole thing seems to have started because Thierry found a few problems with the way registers work, and wanted to address them.
The most important flaw was that after you hit C-x r SPC (save-to-register), whatever key you hit next, you'd save the text into the register associated with that key. In particular, the universal Emacs cancel key, C-g, would not work here: instead, the text or position would be saved to a register called ^g. Similarly, if you accidentally hit "jump-to-register" or "insert-register", you couldn't cancel with C-g (or with any other key), you'd be forced to select a register and it's contents would be jumped to/ inserted (if any).
Secondly, registers can hold text, a position, or nothing. jump-to-register only works if a register holds a position, while insert-register expects a text. Emacs includes a preview of registers which are non-empty when invoking these commands, but it doesn't distinguish - it will show you a register that includes strings as an option for jump-to-register, even though it knows it won't work.
So, Thierry took the time to address all of these concerns, and to address other feedback about the code. The reviewers agreed that these are important changes even though they add some extra interaction, and that the breaking change (having to hit RET after selecting a normal registry, or having to use an extra key to save to a weird register like ^g) are worth the gains. After it was done, and compiled, it was added by the Emacs maintainers to the development branch.
The author of this article came along, asked for a switch to revert between the new and the old behavior, and was asked for a patch. They provided a patch that reverted all of the changes I mentioned before (so, no way to cancel the register commands, no way to get contextual help about which registers contain text VS position, nothing) and instead implemented an entirely different feature (confirmation on overwriting a non-empty register based on a flag). Thierry installed the author's new patch and gave this simple feedback, to which the author basically replied "you don't need all that".
Now, as more people started using the feature, the belief by Thierry and the original reviewers that the breaking change had minimal impact was proven wrong. Thierry started working on a new improvement to create a flag that keeps both all of his new work, but allows the previous workflow too (particularly, removing the extra RET, which was ultimately a side effect, not the main point). The patch missed the mark, but it is still being worked on.
Overall, it seems the process is working quite well, and it is only the author of this article that is trying to bully his way into the discussion and ignore the context, with a very anti-hacker attitude of "if it kinda works, we shouldn't change it in any way", which is very much against the spirit of Emacs.