I really like IU. It would be nice to have the permissions expanded to have what group(s) could not just edit the page but what group could view the page. This would allow for private user group pages.
Currently it's up to users to decide how their links will look like and it's up to them to link their articles from within the editor. We are considering an option to make some changes in IU concept which could break down backwards compatibility but it would make IU better and it would IU users have less problems using/configuring it.
We will also consider implementing private pages option you suggested.