How about using tags/links to associate attributes with requirements?
This could be as simple as adding a link, fo e.g. :

  * If it is traceable or not
    + \[[attributes/traceable]]
    + \[[attributes/untraceable]]
  * Its criticality level
    + \[[attributes/level/critical]]
    + \[[attributes/level/important]]
    + etc.
  * Its priority
    + \[[attributes/priority/low]]
    + \[[attributes/priority/high]]
  * If it is functional or not
    + \[[attributes/functional]]
    + \[[attributes/non-functional]]

You just have to create pages for each attribute you want and then pagespec could be used to filter requirements by attributes. I think something similar is used to trac bug with ikiwiki (linking to a \[[done]] page, etc.).
