Still getting my head around the inline + float layout, but that sounds like a plan. The flow tree for the test above is:

+ RootFlow: (GenericBox  )
| + BlockFlow: (GenericBox  )
| | + BlockFlow: (GenericBox  )
| | | + InlineFlow: (ScannedTextBox  )
| | | + FloatFlow: (GenericBox  )
| | | | + InlineFlow: (ScannedTextBox  )

Would the FloatFlow then become a child of the first InlineFlow, or does the hierarchy above still remain as is (where InlineFlows never have children)?