Many people have a powerful desktop pc in their room for playing games. Usually though you don’t keep your trainer in the same room/office/whatever. You have to buy a second machine if you want to run zwift in an acceptable manner.
As zwift requires quite a bit of hardware, why not just create a mode that, instead of using 3D gfx, shows a simple map where dots race against each other? This way one could use a lower spec machine if it’s only for training.