In reply to Luke.

I think this is a good idea. Seing as closed plugins aren't removed from the repository database, it shouldn't require a lot of changes to the update flow.

As far as I know, when checking for updates, a list of all installed plugins is sent to wordpress.org and a response tells which ones to update. This is also the reason why if you create your own custom theme/plugin with the same name as one in the repository, you'll get an update notice for it.

So I see 3 use cases in the update flow:

1. Theme/plugin is active/hidden in the repository.
Get update notices. (as today)

2. Theme/plugin is closed in the repository.
Get notice about no longer being maintained.

3. Theme/plugin does not exist in the repository.
Do nothing. (as today)