I would miss the Sega characters a lot Sega just has to market this carefully. They have to be clear this is its own thing and maybe try and design it away from what the first two racers established.
Eventually Sega should do more things with Sega IPs, we shouldn't have to wait for the next crossover to see Jet Set Radio, Alex Kidd really almost everything.
That said I would be happy if it means they can expand on what to see in Sonic content and theme the gameplay completely in Sonic's favor.
1. Sonic themed items.
Actually, would be cool if they use shields and their abilities. Covers defense and you can play it smart.
Fire = a fire based speed boost that attacks opponents/badniks, Bubble = able to drive without speed loss in shallow water, Lightning = attracts rings.
2. Obscure and retired characters like Fang and Mighty
3. Large variety of Zones brought back not just the usuals I want to see a Game Gear zone like Sunset Park.