So I had an extension installed that apparently now has been yanked, giving a 404:
https://marketplace.visualstudio.com/items?itemName=Ponicode.ponicode

That's fine that somebody yanks an extension if they want to, but in my VSCode it still showed as installed and even clicking on it just showed the README with no sign of it being yanked.

It made me wonder what other extensions I may have installed that have been yanked? Hard to know.

VSCode's Installed Extensions list should have clear labeling for yanked extensions, just like you already do for deprecated ones.