Well, like any other company, GameFreak's main purpose is making money. It's why they introduce newer generations every few years, why they bring out a third counterpart of the first two releases, why they have version exclusives, and why the eventually bring out their remakes. Not to mention the games that are made for other systems such as the Wii. GameFreak's not making you buy the game if you don't want to, but they are trying to temp you into purchasing their games; especially if it's a remake of a generation you fell in love with.
That said, I just think it's too early to be thinking about a remake of Diamond and Pearl. Platinum itself was only released just three or four years ago. It's hard to say what you'd like, because you don't know what we'll have by then. What kind of graphics the game will have and if it'll be in full 3D? What kind of handheld will it be operated on, and what features would that handheld offer? There's a lot of questions that factor in, so I couldn't really say what I would want.
The games were enjoyable, especially Platinum. Would I mind a remake? Perhaps, yes. Let's just wait some years to see the path Pokémon is taking before we get there.