I also build Wordpress plugins, so this is a great question for me to answer.
I think building an API to add open source code like PHP and HTML 5 would be great. Using a Restful API is the best way to go so web designers can simply send their data to the directEdit plugin and it will dynamically create the website.
I would be glad to speak with you on ideas for offering an API.
I always look for open source APIs to allow me to modify the data