What's funny is that this is not the first time I've heard of a Sonic RPG coming out. Back in 1992, back in a time when Sonic was actually popular and had fans Sega planned to make a game featuring Sonics sister that would be a conversion of a popular Japanese RPG called Popful Mail or something like that. The plan was scrapped after Sega of Japan got nasty responses from fans of said game, but some of the concepts like a pink female hedgehog would enter later Sonic games.
The second time a Sonic RPG was announced was when a group called Panovation Studios stated it was working on a MMORPG based around the Sonic Universe. It ended up being a fraud, but they went to great lengths to make it seem real, even posting on Sega.com's forum claiming to have had interviews with Sega employees about the project.
So there you go, some fun video game history