In reply to djsteveb.

This will only work if plugin authors opt into the new Update URI field. If they don't, it'll be the same as before. The new piece is that the solution is there and takes one line of text in the primary plugin file.

So, something like the spam plugin you mentioned could add the header to avoid checks from WordPress.org. You could do the same for non-.ORG plugins.

As for URL and ownership changes, no. Those are separate things. This new feature basically tells WordPress the hostname to check for updates.