So far the journey of wiki has been very pleasant to me. I liked the wiki concept and technology it focuses. Mediawiki comes with lots of features and extensions which are really cool. But still i feel that there should be some very good features included in future MediaWiki. Here are my few thoughts:
1. More security options, such as section based protection. currently mediawiki have the option to protect a page not a section. we know in multi user environment many people can contribute their part in a single article. there might be the necessity to protect individual contribution rather than the complete page.

2. The wiki editor can be enhanced little bit to add few more options to make life bit easier. It is not right to expect an end user will know the complete wiki syntax to use it appropriately. May be a WYSIWYG in wiki mode will be good choice.
3. Article save and publish option. currently wiki does not have the ability to save an incomplete article. this option will really help the writers to write articles and publish them once its complete.  It will be also nice to have an auto draft options for articles. so that nothing is lost accidentally.

4. an integrated comments system for the article. it can be kept as an option in the article edit section and will be shown in the view of the article page.

5. last but not least , more of a web 2.0 featured. it will be really cool to load contents dynamically using AJAX and give it a look and feel of a web 2.0 site.