It seems that a while ago, Microsoft filed a patent for a video game ”having a plurality of game engines” running at the same time. This patent was filed in December 2011, just after the release of the Halo:Combat Evolved Anniversary game which allowed players to switch from new to old visuals or vice versa on the fly.
Whether Microsoft plans to use this technique for games again is unknown however the patent reads “Remakes of games attempt to captivate their audiences by leveraging the emotions associated with the initial game. However, this may be lost as modern graphics may cause the gamers to lose that feeling of nostalgia. Thus, the very purpose for the re-release of the game may be lost by the “improvements” made to the game.”
So from this it could be possible that we could see more games running 2 or more engines at the same time therefore allowing you to switch from the new visuals to the old visuals to regain that “nostalgic” feeling.