I doubt anything that would only fit in the Stampeded would fit in the M03. The M03 is supertight in the battery compartment. Keep in mind that A123 is a pretty huge battery manufacturer, so I'm thinking the battery you are talking about is different altogether. Maybe a 3s lipo? Also the lithium iron phosphate chemistry was just recently announced, so I'd be surprised if it was around earlier. Honestly, I'm incredibly surprised that this is out so soon in the R/C market! MIT and A123 just went public on this technology only 1 month ago!
The ones I read were these...
http://www.radiocontrolzone.com/showthread.php?t=222362
I think A123 were already making them for other electric devices and decided they might fit in some RC cars. Many LiPo chargers made since 2006 have the option to charge these cells.
They are the superior 'fun' batteries in many ways, but they do lose out in terms of voltage and capacity, so even if they are allowed in races, they wouldn't be competitive.
I sometimes read about them in drag races (where capacity isn't so important, number of cells is not limited, and anything goes for motors) and of course basher vehicles.
Robust, safe but low energy density, like the Ni-Cads of the lithium battery era.