Prerelease:Sonic Generations (PlayStation 3, Xbox 360, Windows)
This page details pre-release information and/or media for Sonic Generations (PlayStation 3, Xbox 360, Windows).
Internal Document
This document was accidentally leaked on Sega's PR site in late 2009, which shows that the game was already in the planning stages by that point.
Aside from using the working title "Sonic Anniversary", it seems the original idea would've been a compilation game with the description "could put out collectors edition with all old sonic games on one BD disc" and that the PlayStation 3 version would've included exclusive content.
Scrapped Wii Version
Aside from the PS3, Xbox 360, and PC versions, a Wii version was planned at one point. It's not known why it was scrapped, though it could be related to the system's weaker hardware compared to the other consoles and PC.
Interestingly, many models in Sonic Colors have an "_SD" suffix, so it's possible that Colors assets were meant for use in a Wii version of Generations at one point.