It would be great to be able to use wiki style formatting and table of content inserts into solutions.
I think the 3 level nesting of solutions is a good limit but being able to add a table of contents to a solution is needed to provide a better overview.
Take a look at the freshdesk API solution info at http://support.freshdesk.com/solution/categories/4/folders/453/articles/167-using-the-freshdesk-api.
imo it's very hard to jump to the right API topic.
Also imagine a situation where you have a solution in the form of Manual > Settings > Users, you would like more nesting for describing how to add users, delete users, etc.