I don't have lots of experience with Wordpress, Joomla, or any other PHP CMS for that matter. But I do know how to build a JSON RESTful API. In this particular case I've created one that handles creative content (articles, events data etc.)
Now I would like to create websites that consume this data. Each website can be a campaign website that retrieves its articles from a central repository a.k.a. the API. I can create content channels in the API that serve as a content pipeline for one particular website.
Normally I would create a website from scratch using HTML/JS and CSS. But I also recognize the benefits that comes with a popular CMS. You can add plugins along-side the articles etc, use tools like varnish and lot of SEO stuff.
What I don't want to do is duplicate the article content to an MySQL database. The articles should be managed outside the campaign websites. I would be very interested in anyone who has experience with a similar challenge, or anyone who might know an elegant solution to this problem.
i do a similar thing with only two sites (Joomla). Basically i have a server where the articles where stored and two hosted domains. I did it with different techniques on the two sites (just for testing) and both work great for a long time.
The first page render the articel items trough a rss-feed (basically xml). The second domain do this via JSONP. As i said both of them do not use their databeses to store articles in their categories, they just display content via http requests and formated data.