All worlds will get the Version 6 updates. Existing worlds will not get army camps, but they will get all the changes that are features, just not those which are settings that are world specific.
When the existing worlds get these features may be a few days or few weeks after W4 opens though.
I have accidently set the 'mobile' settings on w4 and now I can't undo it and am struggling. Anyone know how to remedy it? Went back to settings menu but mobile option now not there