Or they could keep an archive of the annotations and provide a process for the video owners to choose to have Google 'bake' them into the video permanently after they've been shut off from being used by mainstream YT interfaces. Annotation links could be visually represented in a way that indicates their link could now be found in the description.

Too much effort, won't happen. When you care only about view count and not the content, it's easier to just deprecate and delete.

Agreed. I see it happen all of the time.

Note that that won't suffice for the purposes mentioned above, as oftentimes the annotation would, say, replace a specific word in the text; the replacing word by itself won't be very meaningful, as you won't know what it was intended to replace.

It's still more useful than simply banishing them to the void.

How about adding the coordinates in the screen that it replaces? Some percentage distance from top left.

Even I couldn't reliably determine which word was replaced given screen coordinates, and I spend half my time pushing pixels around (web design & photography).

Yeah, in order for this to be usable, it would need a better UI. Maybe some kind of overlay: it could automatically position the annotations at the correct position relative to the video, and make them appear and disappear at the appropriate times.

I wonder if implementing something like that would be technically feasible.

You are proposing rebuilding the existing feature Google wants to turn off.

That's the joke

They could also add them to a specific captions track

That seems like a good compromise to me too. I can't say that I'm sad to see the annotations go though, they were so often abused that they were permanently turned off on my side, corrections or otherwise. I'm not generally a an of breaking things for the sake of breaking things but I think it's a good move on Google's part.

The abuse could've been stopped very easily. The main problem were link annotations, so a simple popup on click, saying "The video wants to redirect you to [url]." "Continue/cancel" would've been enough. Disallowing annotations in a 10% border inside the video and only allowing all annotations to cover at most 50% of the screen on top that would cover all or the cases I can think of.

Limiting their size would cut down on the clickjacking annotations, but wouldn't deal with the hated "buy our merch!" annotations that were damaging to the video content and led to people turning annotations off. I think simply removing all links would be clear and effective, without damaging the error-correction use.

The third common use that I've seen is linking to other videos, and that's the one that YouTube's replacements systems tackle.

Another somewhat noteworthy thing is that the annotation system is tied to YouTube's channel logo overlay. Once the annotations go, it's likely that the logo will not be hideable anymore.