I don't know if this is currently possible, on its way in OO4 or not even considered yet but in principle, I would like a way to separate 'Titles' and 'Items'. In this way items could be managed separately from the outline structure.
For example:
1 The Solar System
1.1 The Planets
1.1.1 Earth
10 - Enslave Male Earthlings
20 - Steal All Women
1.1.2 Mars
1.1.2.1 Setup
30 - Send Male Earthlings to Mining Colony
1.1.2.2 Construction
40 - Build Factory and Mining Complex
50 - Create Golf Course for Slave Masters
60 - Build Sun Surfers
1.1.3 Venus
70 - Terraform Venus
80 - Set-up pleasure palaces
90 - Induct Earth Women
1.2 The Sun
100 - Set up Sun Surfing School & Bar
For example:
1 The Solar System
1.1 The Planets
1.1.1 Earth
10 - Enslave Male Earthlings
20 - Steal All Women
1.1.2 Mars
1.1.2.1 Setup
30 - Send Male Earthlings to Mining Colony
1.1.2.2 Construction
40 - Build Factory and Mining Complex
50 - Create Golf Course for Slave Masters
60 - Build Sun Surfers
1.1.3 Venus
70 - Terraform Venus
80 - Set-up pleasure palaces
90 - Induct Earth Women
1.2 The Sun
100 - Set up Sun Surfing School & Bar