Serebii said:
Na, I have a hunch that another game will be revealed to fill the gap between Ranger (March) and DP (November) in Japan and that that game is the one thats being counted
I must say that it is ironic for the two of us to share the same opinion. If you happen to remember, you started a forum thread in June 2004 pertaining to a mysterious game that was rumored to be announced the following month. You, as many other members, assumed that to be one of the next generation games, despite the fact it would have logically been two games in that case. I suggested the game would be the third game to Ruby and Sapphire, particularly since it was too early for a full-fledged announcement of the next generation. Irrespective of my argument, everyone seemed to have dismissed the idea on the grounds that FireRed and LeafGreen had filled the need for a third game. Needless to say, the game in question was Emerald - Diamond and Pearl were only revealed later that year, and their "announcement" was merely limited to title names.
I am not bringing this up to open a box of worms, on the contrary - I am impressed that after a year and a half you have changed your views on "repetitive" games. It would appear that the majority of players are primarily interested in the sensation of exploration, and by that I am referring to new Pokémon. Granted, the pair of games that define each generation have more to offer, but to reach its potential a generation cannot consist of these two games alone. In other words, the question should not be how much time has passed since the beginning of the current generation (Ruby and Sapphire's Japanese release), but rather, whether nothing more can be done to supplement the generation as a whole.
The aforementioned question was relevant prior to Emerald's release, and remains so to this date. From that time till now, XD was also released and served its role in unlocking some of the unused data, but the validity of the question has been left in tact. There is ample of unused data in the third generation games, and while the same held true for the English version of Crystal, at least the Japanese version could be regarded as being complete. In this case, the Japanese and English versions (and otherwise) are on equal grounds, but the problem lies in that higher standards have been put forth. Most notably, Game Freak developed a parallel series to Ruby, Sapphire and Emerald - FireRed and LeafGreen.
It is plain to see that I am in fact suggesting the purported new game will be a third game to FireRed and LeafGreen. In my eyes, anyone who has played the games should be able to assert that they constitute a series on its own right. That is to say, they go far beyond the notion of adding the older generation Pokémon to Ruby, Sapphire and Emerald. It follows that a third game to finalize the series on the one hand, and the third generation on the other, is well in order.
From a practical viewpoint, I must first stress that none of the current four
Path to Diamond and Pearl games was developed by Game Freak, not even Ranger. As such, the development of these games could not have possibly interfered with that of Diamond and Pearl, which raises the question what else could account for the one-year delay of the games. Observing the past two generations, Ruby and Sapphire were announced soon after Crystal's release in a straightforward fashion. With Gold and Silver, their beta forms were unveiled after Japanese Blue had been distributed, but they were ultimately delayed as to incorporate them into the Game Boy Color environment. As fans had expected the games to be released in 1998, Yellow came as an alternative that was soon deemed the true supplementary addition to the first generation. Thereafter, Gold and Silver were revealed in their true forms (including the names).
Essentially, Diamond and Pearl have always been slated for the Nintendo DS under their current names, but their announcement following Emerald's release was of a different nature - lacking official artwork to represent the games. This fact has not changed since, with the only details known about the games being far too general to count as solid impressions. Presumably, the third game has always been in mind, and the plan is to showcase Diamond and Pearl once it has been released. As for when the game will even be announced, I personally think it would have already been announced had it not been for marketing considerations (potential collision with Ranger's upcoming release).
If to trust my instincts, now that Ranger's release is ever so imminent, the third game could very well be announced in this month's CoroCoro. Furthermore, the Pokémon Wonderland magazine will also be published this month, and assuming it bears the same content as CoroCoro, a preview of its cover may be enough to confirm the game's existence (as was the exact case with Emerald).