The specific model name in question is "CECH-4001x", where "x" stands for different hard disk configurations. Note that Sony's PS3 Slim belongs to the 3000 series, which brought about significant size, weight and consumption improvements to the previous version.
It is thought that the new model will be an even slimmer and cheaper version of the company's popular console. PlayStation 4 isn't expected until the end of 2013 and Sony seems to think the PS3 can be milked for a bit more, the slimmer version being a perfect candidate for such a move.
Although it's not quite an actual proof, Eurogamer quoted one Sony's executive who, when asked whether an even slimmer version of PS3 is possible, said "Never say never". He pointed out that hardware guys always look for ways to make devices smaller and cheaper, but we guess we'll see soon enough.
More here.