Show Requirement rank in List view (and API)

Currently you can assign and view the rank of a feature (drag and drop to reorder, show Rank column in List view).  You can also drag and drop Requirements within a feature today, but there's no way of showing that ranking.  This would help us to full utilise the prioritisation and reporting at a requirement level.

1. Feature A

   3. Requirement X

   1.Requirement Y (most important requirement within Feature A)

   2.Requirement Z

2. Feature B

  1. Requirement I (most important requirement within this Feature B)

  3. Requirement J

  2. Requirement K