I am going to be developing a web application that interfaces with a horse betting website (via its API); it makes automatic bets given criteria is met, queries the API to receive and display race information and has the general login/logout/user management functionality. My first inclination was to use Angular.JS and PHP.
The client asked me whether it could be developed as a WordPress plugin as it would be easy to sell, the client doesn't need to host everyone on his server (customers install it on their WP website) and for non-technical users to install. My first thought is that WordPress is too lightweight and unsecure to use. But the more I think about it, it could work, the user management is already implemented, there are many WP payment plugins.
So I am looking for software recommendations for a horse betting web application (given the requirements mentioned above) and if you think a WordPress plugin is suitable for such an application in terms of security, functionality, meeting the requirements and etc.