Multi language wiki
I think one important missing feature is to support multiple languages in the wiki.
Each wiki page could exist in one or more languages. The user should see the page in his most prefered language, if available. In Switzerland, for example, we have 4 offical country languages plus English. Providing some or all pages in those languages by naming them 'page1_EN', 'page1_FR', ... might be a solution, but the suffix should be hidden from the user and the proper language should automatically be picked when the user opens the wiki page 'page1'.