It's certain that 2 years from now extension developers will still be getting support requests and receive negative reviews because of that commit, even if an alternative API is released in the next few months. But who cares, it's not you who has to find a solution and deal with users.
All of this could have been averted by simply offering an alternative API in the same browser version in which the new restriction was implemented. There was no pressing need to immediately restrict the API.
> Disallowing the modification of Access-Control-Allow-* response headers will impact extensions that need to download page content.
> Search by Image sets CORS headers for some images in order to download them from the content script before uploading to a search engine. In many cases an asset will only be served if the request contains the correct origin, referrer and cookies. Reproducing such a fetch request was impossible from a background page last time I tested, and even if configuring all aspects of a request becomes possible, it could still open up extensions to security issues, because it's difficult to figure out if certain data types would be sent by the browser if the request would be made from the page context, such as the referrer. We would also need to request additional permissions, such as access to HTTP cookies.
> Extensions used for archiving pages would no longer be able to create faithful representations of the tab content. Advanced ad blockers such as uBlock Origin would be impacted as well. There is a general issue of extensions not being able to access certain parts of the page, such as a tainted canvas in Chrome, or a closed shadow DOM in Safari, and this restriction would make the problem worse.