I think a few Nintendo DS games can fit for Dreamcast. Like Nanostray 1/2, Dementium 1/2 , Golden Sun is the games i like to see on DC. Of course if JoshProd is smart then can bring them on Dreamcast.
Hey, just today Rubberduckycooly released a decompilation of the PC 2011 port of Sonic CD, it seens to be based on SDL2 and maybe could be possible to port for the Dreamcast!
Sappharad who was listed in the credits for this was also working on a version for PC and Dreamcast. He told me last year it would be worked on, so we are definitely getting a port of Sonic CD one way or another.
Here is a very early WIP build running on DC from 2017.
I know it's ancient but I think it'd make a brilliant multiplayer game. Also, would Microprose's GP500 or EA's Superbike 2000 be possible, technically I mean? I have no idea at all but I think they'd be a good fit on the DC (a sort of arcade/sim like Le Mans 24H.)
Thinking a little outside of the box in a more home-brew way rather than a fully fledged indy release, but Sonic CD shown there with assets that made up Sonic Mania would be awesome, I am assuming Mania to be based roughly around CD , although it's probably nowhere near that simply put... Also, SOR4 recreated in Beats of Rage would be a dream.
Sonic Mania isn't based on Sega CD, rather the engine was made originally back in the day for the Dreamcast by Chis Whitehead as the Retro Sonic game demo that was built in the official Window CE SDK. Chris then ported Sega CD over to this engine and recreated the game in it. Sega was so impressed he got to make his own more fleshed out game from it.
In fact, some people ported the old Retro Sonic stages from DC to the PC version of Sonic Mania you can see below which shows how the engines are the same.
If anybody wants to play the original Retro Sonic you can try it out here.
Also, Tom from the DCJY asked Chris Whitehead theoretically if Sonic Mania could possibly work on the Dreamcast. You can see the article here. And yes seems it could.