I discussed workflow a bit in another thread, but to address more specifically priorities in OmniFocus, I'll say that OmniFocus does not need a dedicated data bucket for priorities. What OmniFocus could benefit from is tagging, and Ken has said that user-defined metadata is coming. Then the user can create tags for priorities or whatever the users believes is valuable. Frankly, the time estimate field in OmniFocus could be consolidated with the tags metadata if there are no future plans to incorporate math functions in OmniFocus (for example, a project's time estimate is automatically calculated from the time values of the individual tasks).