If it would be this easy then i would’ve long done it. But that it’s something really complicated can be seen at the fact that even the Blender developers didn’t do it yet. Outliner improvements are at the table since years.
It’s not an easy fix, it’s not Python. This is one of the many areas where you need C code. When you want to change something here then you need to go across several c and h files, with mainly uncommented so called self explaining code. Something to go mad about it. That’s why i avoid to touch Blender core functionality where ever possible.