A Famitsu interview with the SEGA AGES devs that was translated by Nintendo Everything has provided more info on the upcoming releases. Some highlights are below, but I highly recommend you check out the link provided and read the entire translation.
For Sonic the Hedgehog, they’re adding modes included in past ports such as Ring Keep and Stage Select. But for the first time they’re also adding the ‘mythical’ arcade Mega Play version as well. They also plan to add even more detailed gameplay features.
In the closing messages, Shimomura was noted as saying that they eventually want to aim to cover “all of SEGA’s titles!”