Hmmm... I was only going to create a new thread for these, but new evidence has come up suggesting these are legitimate.
Of the before-mentioned CoroCoro pages not scanned yet, apparently a collage exists showing all of them:

Of note, take a look at the lower-right page. There are reportedly mysterious pokemon silhouettes being advertised at Pokemon Platinum pre-order booths. Apparently, there are a couple variations:

I'm not sure it's confirmed that these are 5th gen pokemon nor new pokemon forms in the 4th gen, but the most interesting suggestions I've read thus far (on Smogon) posit a connection with Rotom. From his Pokedex entry:
Quote:
Its body is composed of plasma. It is known to infiltrate electronic devices and wreak havoc.
The suggestion is that Rotom could gain the ability to possess some electrical appliances to "change forms." That would be pretty cool.
smile (Also noteworthy mention... orange silhouette as a potential sandstorm version of Castform? Also from Smogon.)