As far as you know, is there any truth to the long-standing rumor that a third "Adventure Sonic" was ever considered for Sonic Generations? I don't remember anyone drawing a distinction between "Modern Sonic" and "Adventure Sonic" as characters circa 2011, so it always sounded like one of those rumors that held on thanks to wistful thinking.
To my memory, the information comes directly from Ryan Drummond himself, who stated Sega was offering him the role of Dreamcast Sonic for Sonic Generations. He declined because he said Sega's offer was an insult; they wanted him to leave his actor's union and were proposing to pay him way below the going rate.
Digging, it looks like the source is a (now defunct) website called The Gaming Liberty. Here's a Wayback Machine link. However, it doesn't mention anything about Dreamcast Sonic, just that Sega was trying to get him back.
Doing some more digging, this Game Informer article pointed me towards an episode of Did You Know Gaming.
Watching the video, they tag the information to Unseen64, who claim to have "sources inside of Sega" that confirmed this detail for them. For what it's worth, Unseen64 seems generally accepted as reputable as far as I know. The article's byline is one Liam Robertson, who has a history of significantly more hits than misses when it comes to leaks and insider information.
Liam, incidentally, now works for Did You Know Gaming, and a lot of their more recent videos involve them publishing original research received directly from the developers themselves -- much like Unseen64 used to do (and still does, I guess).
For me, I always felt a pretty clear delineation between Dreamcast Sonic and "Modern Sonic." Sonic 06 was an attempt for them to do Sonic Adventure 1 over again, and when that failed, we got Sonic Unleashed, which to me plays absolutely nothing like Sonic Adventure. All that talk where they say "we called unleashed 'sonic world adventure' in japan because we were trying to make sonic adventure 3" feels like marketing garbage to me.
There's a feel to Sonic Adventure. A vibe. If you could truly touch the heart of Sonic Adventure with your fingers, you would feel a certain kind of texture. Sonic 06 has a very similar texture and Sonic Unleashed does not.
Sonic Unleashed was the soft reboot Sonic 06 wishes it could be, and there is an unmissable line in the sand drawn between the two games. Sonic 06 was the last gasps of an old era and Sonic Unleashed was its rebirth as something new.
