At the SXSW Sonic panel, Sega teased a new Sonic racing gaming with a Sonic-style logo that emphasized the R.
Not much was said beyond that game, except Sonic social media manager Aaron Webber emphasizing the game is not a sequel. This is likely in line with his previous comments that a new Sonic & Sega All-Stars Racing Transformed was not a thing, though a Sonic-focused racing title seems to be close enough that a denial at all seemed unnecessary.
The initial teaser trailer showed car headlights being panned over, so it looks like Sonic is back behind the wheel once again.
While it is not known if Sega is developing this internally or not, a leaked powerpoint from developer Sumo Digital, who made the S&SASRT games, indicated they were working on another kart racing title, which is what lead to these rumors in the first place. It seems likely they are working on this game, as well.
Sega has not announced when the next details of the game will be released, but with E3 in only a few months, that is a safe bet.
Hopefully the new game differs itself from Sonic & Sega All-Stars, if only to justify not having a lot of the cooler aspects of that game in a new title.