Pokémon Brilliant Diamond and Shining Pearl are faithful remakes of the original Pokémon Diamond and Pearl. As such, content from Pokémon Platinum is notably absent from the remakes, much to fans' disappointment. This then raises the question of whether or not there will be a remake of Pokémon Platinum.
There is no official word suggesting a remake of Pokémon Platinum is coming. Looking at past remakes in recent years, it has always been the two versions that are remade, but not the third entry. So, it is very unlikely that there will be a Pokémon Platinum remake any time soon.
One thing to note: The Pokémon Company and Nintendo are developing DLC for their games with greater frequency. Pokémon Sword and Shield received two different DLC that added content to the base games. With that in mind, if any content from Pokémon Platinum were to come, it would likely be DLC.
But no word of this has been mentioned, so take our theories with a grain of salt. For now, fans can enjoy Pokémon Brilliant Diamond and Shining Pearl for what they are—remakes of Diamond and Pearl.
For more information on Pokémon, check out How to get the National Pokédex in Pokémon Brilliant Diamond and Shining Pearl and Pokémon Go Mischief Unbound: Event Details, Spotlight Hours, and Raid Hours on Pro Game Guides.