Here's what H2A is running simultaneously: Two game (graphics) engines - the OG H2 and H2A, and the original audio (music and FX) and completely new music and FX. And the switch is instantaneous. If it weren't running the OG engine it could in theory run at a higher resolution but that's not the intended nature of the project. It's designed to be a remake that lets you switch between the two instantaneously. Now you can feel one way or another about that, but that is indeed the intent.
Since this thread is about the resolution, these are all fine conversations to have, but iI hope the community thread is talking about the content, not the pixels.