LB: I've always said that if you're going to release a remake / remaster, you should ALWAYS include a playable version of the game in its original form. The Halo remasters have been fabulous for this, allowing you to switch at any time during the game. The Monkey Island and Day Of The Tentacle remasters do as well. Can't think of any other examples off the top of my head, which goes to show it should be a more common practice!
Happy to say we walk this walk by keeping the original Apple II Wizardry interface accessible at all times. Toggle it full screen, lower right corner, or off completely, but it's always available because we're running a ported version of the original Pascal code underneath the Unreal Engine.