I've been thinking about this market lately, have you done something similar?
There are also some excellent plugin markets for most eCommerce platforms if you've got the drive to develop in them. Companies using an eComm platform are likely to be actual businesses so they are willing to spend more money for a quality plugin.
The other option is building a SaaS app and using a single WordPress install or WordPress multisite as the platform. I thought this was a crazy idea a couple years ago. Now I know of dozens of apps that have WordPress as the back-end, and it works well.