Uh...they are remakes of ruby and sapphire for a reason. They are suppose to be similar. There could have been more Emerald stuff but GF chose not to so the games would stick to the originals. ORAS are decent games in my opinion.
Expect GF to do the same with DP remakes. They would be remakes of Diamond and Pearl. Not Platinum. Sticking true to the originals is what remakes are about. Remakes usually updates the originals games.
At least DP with a Platinum episode will feel more natural than just shoving all of the Emerald nods (but not the features) until after the main game. Just think about it. Would Cyrus
really give up after failing with one legendary? I don't think so. The post-game scenario would probably have Cyrus attempt to use the other mascot after escaping from jail, only for Giratina to swallow him up with the player into the distortion world. IT's actually also a lot less random then Giratina jsut swooping in in the middle of Cyrus' plan with no context. Attempting to do the same thing twice, however, would be more likely to make Giratina pissed. In fact, I could even imagine that some of the Ultra Beasts might have moved to the Distortion World and ended up becoming more bizarre there then they were before.
Whatever the case may be, they better at least have Platinum's regional Pokédex expansion, as the poor Pokédex distribution and the fact that some of the newer Pokémon relegated to the post-game national dex were a major criticism fans had in regards to DP. No matter how much Game Freak want to stay true to the originals, giving us the same poor regional dex will not go over well in regards to those who criticized Sinnoh's poor distribution in the first place. In fact, doing so might even cause Game Freak to lose sales. At the very least, they should retcon some Johto Pokémon already present in the original DP regional Pokédex into Sinnoh Forms so we have more variety in terms of types.