So, it's no different to any of the random holding pages Amazon creates for things that don't exist but they perceive there to be interest for, e.g. West Wing blu-ray which has never been announced yet has had an amazon holding page for at least a year.
So, basically maybe there is or isn't a PS3 slim, but I don't think this is evidence for it... Sorry.
Sadly, this is no confirmation of the PS3 slim at all. "Melden Sie sich an, um per E-Mail benachrichtigt zu werden, wenn dieser Artikel verfügbar ist." simply means "sign up to be notified when this item becomes available".