They seem to have at least two Transformers exclusives at SDCC, and a second one has been announced by Hasbro.
The Mighty Muggs Optimus Prime figure is being done up in a metallic colour, and given special packaging.

Hasbro announced it on their news site here, but since that is difficult to access for non-Americans, the tfw2005 website has the photo and details mirrored here.

Thanks to the admin of the Mighty Muggs Forum for also sending me a message on this news item to post here.