A slimmer version of the PS4 might have been leaked, and the alleged new model is currently on sale on auction site GumTree (the link is provided exclusively for crediting purpose. We wouldn’t encourage the purchase of products with questionable sources).
From the pictures provided by the sources above, which you can see below, the console appears to have actual mechanical on/off and eject buttons, and the product code CUH-20XX, which fits Sony’s coding standards for a redesign of its console. The last two digits indicate the region of sale, in this case 16, which correctly matches a model for the UK market.
It also appears to have no optical audio port, unless it’s hidden really well. On the other hand, it retains the disc drive.
Of course, we should still consider this a rumor, as we have no way to fully verify the authenticity of the console. Incidentally, no documents about it appeared on the FCC database as of yet.
If it’s real, the “slimming down” of the form factor is actually rather limited, which is unsurprising, considering that the original model is already very small.