It's already confirmed to not be emulation. They've also already released the games through emulation many times, such as in the SEGA Mega Drive and Genesis Classics collection.
I'm hoping that they are porting the recent mobile versions of Sonic 1 and 2 (or at least including the same features such as additional playables, better special stage graphics, widescreen, etc.) and at least taking inspiration from Sonic 3 A.I.R. These are the best ways to play the games currently, and I'd be quite satisfied with a bundle deal that bumps the games up to that standard of quality for a larger range of devices.