Pokemon Diamond and Pearl originally released for the DS back in 2006, making it over 15 years since the games debuted. Fans have been clamoring for remakes for awhile now, and there's been quite a few rumors about that request making its way to Switch. While we still don't have a confirmation from Nintendo or Pokemon Co., the rumor has once again popped up.
The Spanish Pokemon fan site Centro Pokemon is saying that sources close to the project have confirmed that Diamond and Pearl remakes are indeed being worked on for Switch. Apparently we'll see the reveal of these remakes in February at some point, and they stick more closely to the original games than Pokemon Let's GO did with Pokemon Red/Blue.
Adding fuel to the fire, it seems there's something going on with the domain diamondpearl.pokemon.com. While you get a 403 error when visiting, this is different from domains for other Pokemon games. Trying to visit both blackwhite.pokemon.com and http://rubysapphire.pokemon.com give you no return at all.
Is this all just speculation, or are we actually nearing a reveal? February isn't far off, so I guess we'll all find out if this rumor is true or not soon enough!