It would be less of a port than a recreation of RE5 using RE4's development, planning, and resource management processes. Recreate the assets for the RE4 engine, start in a relatively bare-bones setting, then include more objects as available resources allows.
Dead Rising took the opposite approach and went to hell: it tried to shoehorn the mall architecture/floorplan/loading structure onto Wii hardware, overshooting the available resources. RE4's structure worked as it did because the architecture (and thus the size of memory-loaded rooms) was limited accordingly with the GameCube hardware in mind. So in Dead Rising's case, a lot of resources are being sucked into rendering the different shops and shelves and nooks and crannies, leaving little for the actual zombie models and character counts. A complete custerfluck.