Future is always uncertain and can never be assumed. But future of open source looks bright.
Since last 10 years, open source has achieved a good place onto the enterprise scene. Like many other developments in IT even open source have actually come out from nowhere. First it was misinterpreted of being of low quality or unsuitable for some serious development but now with open source CMS such as WordPress, Drupal, Joomla and many more are considered of much high quality.
If the open source model continue to grow like this than open source projects will adopt more structured traditional methodologies as its development will also mature with the time. In my opinion the future of open source CMS is going to be much more powerful and established than it is now. More and more people are adopting them as they find it simple to use comparatively and also its performance is improving day by day making it more popular.
These days more people prefer to use open sources because of its flexibility and functionalities. So we can say that the future of CMS is going to be simple, extendable and easy to implement and update. The real future lies in modularity and flexibility. We can utilize Content Management System in blogging platform or for e-commerce engine or for a social network.
The popularity of open source has already proven that they are great idea and they can stand easily on their ground in competition to anybody.