In any incomplete game, there will always be some kind of placeholder to be used in the place of actual assets. While I never made any games, it still held true for any kind of creative outlet. Hell, even at work, there's still some kind of placeholder system for a missing piece of equipment or broken machine that would fulfill the function of the malfunctioning part. But while placeholders could sometimes work for the time being, they should never become the thing that they were meant to replace in the first place. One shouldn't expect duct tape to keep two sides from falling apart when a screw was meant to do its job. In the same vein, a placeholder asset shouldn't be in the final product unless it actually looked good enough in the first place.
Then again, there was nothing more permanent than a temporary solution.
"Shizu! Use your eyes!"