There would probably be demand for a more expensive, higher-quality service. Someone else in this thread mentioned adding eye tracking. It also might be useful to add multiple trials from random individuals and create some sort of aggregate statistics. These are both things that you could charge a large premium for.

What is cool about this site from a business perspective is that it is a low-capital, low-cost way to do things with just one person, much like girlinyourshirt.com