This came to my attention on another board. As with every other generation of the Pokemon franchise, the Fourth, Diamond and Pearl, will get their own cousin for the DS, Fall 2008 (in Japan)!
The new version: Platina. Just like how the other 3rd games focus primarily on Legendaries, the focus here appears to be Giratina. And it has a new form, it seems.
When this eventually comes out in English, I will happily return to my schoolboy roots yet again.