While looking at the source for base.google.com/base/processstep1offer, I found references to "trog" (Trogdor) -- the engine that lets users create webpages using Google Page Creator.
Even though these references are in the source code, nowhere in Google Base can you create items with more than simple text. It is possible, yet only speculation, that Google Base will give users the ability to create items with an editor similar to the Google Page Creator. This feature would also make a lot of sense if Google is actually trying to compete with eBay.
There are a couple of reasons some think Google is looking at eBay with wide eyes. Last month, Google announced they are testing a new feature that lets users sell items directly through Google Base. Not only that -- there are now screenshots floating around that reveal a user rating system is in the works. If my suspicions are correct, the addition of this "rich item editor" puts Google Base on a more direct crash course with eBay.