Okay, let's clear up a misunderstanding. This not an /either/ GPUs /or/ CPUs issue here. SDL2 adds windows, textures, and renderers. But it still supports surfaces, even screen surfaces. So a Pygame 2 will add new object types for the new features while keeping surfaces, unless we no longer want image file support or text on the screen. The only big compatibility issue I see is that events are reorganized in SDL2. I emulate SDL1 events in my patch set to maintain backwards compatibility.
The real question is do we want to add SDL2 features to the existing Pygame code base or pull a Python 3 and redesign the Pygame api for ascetic reasons.