Among the pre-merged games was Sonic Nexus which was the only other Retro Engine game with a playable demo. It all ends there, unfortunately. I would argue that Sonic Advance 1 is the closest thing to a proper Sonic 4 that we have. I know Dimps developed it, but that was shortly before they began to lose sight of what makes 2D Sonic work. As much as I would love to see a Taxman port of Sonic Advance, I wouldn't mind if they ended the ports at Sonic 3 Complete (as opposed to Sonic 3 & Knuckles) and went on to make new 2D Sonic games. If they decide to redo Sonic 4, I hope the Episode 1 levels are remade into something beyond Sonic 1 and 2 rehashes. For example, Splash Hill could be a grass level with some water park elements such as Tidal Tubes from the fan game Sonic Zero Remastered, hence the "splash" in the name.