It can be. As long as the plugins you develop solve a problem that enough people are having. Also anything you create really needs to solve the problem easier, faster and better than any free plugins available.
Most of the money comes from creating free plugins with the basic features and if the client needs more features, he needs to buy a premium account or pay a one time fee. This usually works best as the clients can try out your plugin before buying fully.
Dont think it will work, as individual or even developer have tendency to search for free WordPress plugins, they are not willing to pay for plugins which cost are superior than their complete project cost.
I would agree with ORLOVA...the segment is too much saturated. People have almost all the plugins for any thing they would ever want to do with the WP. Most of them as described above use the upselling method. Give basic features and you can ask the user to buy premium ones. But you never know you might be having plugin that is required by certain niche which is also willing to pay. But I highly doubt you have such plugin.
It works, if you are solving the problems that are faced by the populace. And if you are solving that problem in a faster and easier way than the free plugins than you'd be able to commercialize it as well.
So, go ahead with that idea. You're gonna rock.