I'm with George on this one. Sonic 3DS will either be a portable adaptation of Sonic Anniversary or it'll be a new title. Sonic Anniversary will most likely be an HD consoles exclusive, considering Colors was Wii exclusive and I can't imagine Sonic Team having the resources to develop a Wii version of an HD game while also developing Colors. Most likely, the 3DS game will be what Nintendo fans get for Sonic's 20th. And having said that, I think it'll be the portable version of Sonic Anniversary. SEGA seems to be in love with the idea of a portable version existing alongside Sonic console games (see SASASR DS, Sonic 4 iPhone, Colors DS, Sonic Winter Olympics iPhone).
Also, I don't think Colors HD will happen, mainly because I think SEGA would be more interested in moving forward and improving on what worked in Colors rather than rereleasing the same game in a higher resolution. Also, I think they'd much rather have all focus on Sonic Anniversary next year rather than focusing on Colors HD and Anniversary.
Sonic 4 Episode 2 is obvious.
I'm with Sharky on SA2 coming in late 2011 to the Dreamcast rerelease collection. Note to SEGA: have it be in widescreen and allow us to transfer Chao data from SA1 to SA2.
As for Sonic Anniversary speculation, man oh man where do I begin? I'm really pumped for this title! If Sonic Team takes what worked in Colors, infuses it with the classic Sonic visuals reimagined in 3D (See SASASR's Sonic tracks for how I'd love to see the environments imagined, especially the Death Egg track) and has Sonic, Tails and Knuckles with their classic moves, then I'm all for it.
Sonic Colors proved that multiple paths can work very well in a 2D/3D Sonic game, and instead of needing wisps to access these paths why not have paths accessible via Knuckles and Tails? I know rumors were that the game would revisit stages from Sonic 1 through to the Dreamcast days, but I really hope that isn't the case. I hope they don't actually copy stage layouts of old and just slap a 3D look to it. I'd prefer to revisit classic areas if the plot calls for it and see new layouts.
For example, Eggman is heading to South Island to retrieve something from his destroyed Scrap Brain fortress and Sonic follows him. Sonic runs through a new area of South Island that resembles Green Hill but it isn't the same area as before. Or maybe Eggman returns to Angel Island to steal the Master Emerald and Sonic races through a 3D area that plays much like SA2's White Jungle but resembles Mushroom Hill and features a totally new layout.
Basically what I'm trying to say is that I'd prefer to see the plot dictate why we'd return to classic areas rather than simply have places appear for the sake of appearing. And I think were the plot to move the players from classic areas such as South Island and Angel Island through to SA1&2 areas like Station Square and City Escape, it would make for a great way to tie the past 20 years together and make Sonic's world seem more cohesive. We know Sonic has adventured from the islands of the Genesis says through the cities of the Dreamcast days and the expanded world of the current gen games (and even in outer space as seen in Colors), but we've never seen all of those locations connected. Anniversary would be a great opportunity to do so.
I still remember one of my favorite Sonic memories being the unlocking the 3D Green Hill in SA2. Seeing the cursor jump from City Escape to an off coast island that featured Green Hill was really awesome and made the past 10 years (at the time of the game's release) seem much more like one series.
