If Proof of Space is really made a different chain and explodes it will be more like GPU or at least it will be much worse than GPU since RAM is essential to a computer. It needs RAM to work, and GPU on other hand computer can work without GPU.
But the real question is whether we can make a chain based on Proof of Space and replace the great traditional mining ex. Bitcoin Mining
But have you every try using computer without any GPU? Using CPU for 2D graphic and playing video would lead to poor performance (30 FPS or lower) even when you have fast CPU. I already experience that since i tried using Windows VM without any GPU acceleration.
Even with current Proof of Space/PoS which use storage drive, it only cause quick shortage since PoS miner realize they need SSD with very good quality/durability. So i expect if coin which use algorithm which stress the RAM become popular, people would buy high-end or pricey RAM which won't lead to shortage among average computer user.