I have created and finished testing a package that allows customers from ebay to checkout there auctions through magento. Only i am not sure how to package it up for distribution. I have 2 cms pages and a custom block extension.
Well it may sound horrible but i plan on charging for it. Not a lot since you can get your own api keys for free now. Plus i plan on also making an admin integration to post to eBay. I looked at the site you posted earlier but the instructions are only for listing your commercial extension, not how you package one up and distribute it.