Even if it will be practically possible to build quantum computers for average users (given they currently rely on complex physical experiments, one can doubt that), there's the question of whether there's a need for "mainstream" quantum computing.

As has often been said, quantum computers aren't some magical thing that makes every computation faster. They are faster at some very specific problems like breaking cryptography (I doubt that there's a mass market for decrypting the old WIFI traffic you stored from your neighbor, and, these days, most internet traffic is already pq safe) and simulating physics (also probably not something average joe wants to do every day).

In all likelihood, quantum computers will be specialized devices used, e.g., by scientists. You may be able to rent your quantum computing time if that gets cheap enough to be practical, but I doubt many people will ever own one.