"As far as I know, there's been no public discussion of this change, and Google employees may have accidentally leaked the information to me in my innocuous bug report."
There are constant changes to Chrome and these get pushed out in "updates" to selected groups of users, aka "Field Trials". I have never seen any public discussion of any of these changes prior to including them in automatic updates. What makes this change to user control over site data any different. In fact, I can recall years ago Chrome used to let users change Javascript and Cookies settings on a global or per site basis, and from the Address Bar not only a "Settings" page. Then, without any discussion or debate amongst end users, Google changed Chrome. (Note Javascript is needed to store site data via "LocalStorage".) Today, in "Guest mode" on a Chromebook, it's impossible for the user to disable Javascript or Cookies globally in Chrome. Being logged in to the Chromebook is a prerequisite for globally disabling Javascript or Cookies. There is never debate on these design decisions. These are dark patterns. How effective are user complaints at influencing Chrome development. Please cite evidence. Perhaps what we need are user-controlled solutions.
Side note: I can remember a time when it was considered a monumental task to get the entire web-using population to download a new/updated web browser. Almost like a flag day. Today, there is no need for a campaign to get users to "install the latest version of [web browser]." The concept of automating updates is great, but I am not a fan of today's software using "automatic updates" because the way in which developers are using it is user-hostile.
"In my opinion, this change is very unwelcome. It takes away a lot of information and control from the user. For what benefit?"
BEGIN Devil's advocate/"Google's advocate"
Since this is "the orange site", usually it begins with something like, "Googler here. Opinions are my own not Google's."
Our confidential studies show that individuals like the blog author comprise a minority of Chrome users. The majority of users are not aware of such "issues"; they do not publish blogs or give feedback to Google. By all accounts the majority remain satisfied with Chrome as they are not switching to alternatives. We have dominant market share. Our focus is on delivering the best experience for users. Lucky for us, this also happens to be the best experience for our customers, advertisers, and therefore the best outcome for Google. Its win-win-win. It would not be an efficient use of our limited resources to offer a version of the Chrome browser (e.g., field trial) that met the requirements of this blog author, but failed to meet the evolving requirements of Google. Altough we provide free services to our users, we are a business not a charity. If we fail, then the entire world suffers. However we are continually experimenting with improvements to the browser, e.g., based on lawsuits that governments file against us, and we are testing them on various segments of our user base, without needing the user's prior approval for every update. We believe this is the best use of Google's limited resources.
END Devil's advocate/Google's advocate
The orange site commenter's task should be to refute the Google advocate (or defend it). Or even better, give us a more entertaining/thought-provoking Devil's advocate. A fundamental rule of negotiation is that if one can understand the other side's arguments, then she will be far more effective at advancing her own arguments. ("It's difficult to determine Google's motivation for this change." Maybe that's intentional. Maybe Google does not want to open these decisions up for "debate" or negotiation with those affected, i.e., end users.)
"I hope to spur a public debate about it and give some pushback to Google before they make too much "progress" on the change in Chrome."
Good luck. Can someone remind us when that has ever worked before in bringing about changes by Google for the sole benefit of users.
With Privacy Sandbox/FLOC, it appears that debate did stop other browsers from adopting it, but it did not stop Chrome from adopting it.
The more interesting question IMO is what are the possible solutions and how well do they work in practice. For example,
1. Stop using Chrome
2. Use some Chrome extension that "solves" the problem
3. Complain about Chrome on a blog or in a forum and hope for the best
Personally, I have chosen to control site data outside the browser, using a forward proxy. The proxy software does not automatically update itself, it does not run "field trials", and it is not being sued by dozens of goverments. I do not have to make complaints on a blog to try to influence its development. Unlike a web browser from an online advertising funded entity, I have reasonable control over the operation of the software. Through the proxy I can control browsers like Chrome, including headers such as cookies and clear-site-data (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cl...). Nonetheless, I fully subscribe to #1 as the current best solution.