Interesting idea.

First off, if implemented, I would say have a new thread created automatically for new applications. This could be done with some kind of "DownloadsBot" account, and all new threads would go in the Applications forum, I assume. The new thread should contain all information the downloads page does, including a link to the downloads page.

As for major version releases... I think it's a simple matter of comparing version numbers. All applications should be required to follow the versioning scheme (major).(minor).(bugfix)-(package revision), as is stated by the packaging guidelines. Then, we just check if the major version number has changed. If it has, start a new thread, because old comments probably don't apply anymore. For minor versions that fix a bug someone commented about, people can edit their posts.

The next question is: do we want to use these threads only for review, or also for general discussion about the application? If only for review, a new forum specifically for these threads should be created. I would recommend this case, because I imagine the last five or so comments being embedded on the application's page.

Of course, all these comments assume that this system will actually be implemented. Is there a reason for moving over? Is there a specific problem with the current system that we want to fix by doing this? If it ain't broke, don't fix it. I see the "bridging the community" point, but is this really better?