It'll change the ESRB/PEGI/CERO rating if it was put as extra game in SxSG which limit its target market.
Then sell it cheaply as a separate game! And don't tell me they won't because it's not marketable enough, or else we wouldn't have fan-projects such as
16-bit Sonic Triple Trouble,
Project '06 or that mod to make Sonic Free Riders playable by controller.
Sonic Team claims these old Sonic games are lost causes and non-profitable, but fans are not only showing that there is still a legitimate interest in these games by remaking them for today's audience, but they're doing it for free!

If they had re-released Shadow the Hedgehog on Steam at around £10-20, I doubt that alone would be worth it for Sega. But if they re-released during F:YoS, it would likely sell a bit more than any other day, not by much granted but will still make a bit of a tidy sum next to Shadow Generations' profit.
But hey, I'm just a guy playing the fan-mod
ReLoaded version for free, so what do I know?
Yeah, didn't expect TMNT, Spongebob, and Pac-Man to show up too.
Same can be said for CrossWorld game itself.
Strike! While the iron is hot! Use that energy to fulfill your dream!

Aliens are always landing there too. Even baby Superman.

https://www.youtube.com/watch?v=GdJeFB-_PTw
The only guest character in CrossWorlds that could get away for not having voices.
That's Amigo, not AiAi.

Also Amigo already has a PC game version. Not on Steam though.
Yeah, but it's on M-M-M-Meta.

-If you don't start running, nothing will begin-
https://www.youtube.com/watch?v=GV8Soaiye1I

Picture by Rechi: https://x.com/Rechi_C
It's all well and good if you ain't fat or live a physically active lifestyle.