From their official Facebook:
The only thing more surprising than seeing an official post from us here is our announcing that S2HD is no longer dead.
You read that correctly: work has once again begun on Sonic 2 HD! That said, we'd like to give you all a brief tie-in for recent events leading to the project's reboot.
As many of you know, the leading reason behind the project's cancellation was due to the programming element being removed with no possibility of return in its existing form. As of last year, this changed. Before anyone raises the question, no, the former programmer and the S2HD team members have not had a reunion; instead, a fan of the project independently created and submitted his own engine to Vincent, the project leader, for evaluation. After integrating the art assets from the alpha release and successfully testing it, Vincent began to let the rest of the prior team members know, and we've picked up where we left off sans those who are unavailable due to real life obligations. Two other talented programmers have since offered their skills to recreate the game's physics to match the original, and to port the game to the Mac OS platform (the latter of which is still in the earliest possible stage, and we have no estimate on when it will be playable, so stay tuned!).
In response to some of the questions we have seen, the Alpha Release build is officially discontinued and will not get any form of support as we do not have the source code. The next release will be entirely new programming from the ground up.
We'll provide more details in how you can help us out in the next few days. It's good to be back!
So hopefully this time around is more prosperous then the last time. but we'll see...