■Directives have the capability to be account-wide currently, we just don't have any defined that way. For consistency our approach has been that directive SCORE is account-wide, but individual directives are all character-based.
I can definitely see a directive set though that might go into its own category "Account" that has you do things like get BR 10 on 2 different empires, then 3 different empires, or fully complete all three ES MBT or ESF trees. Those type of directives might make for good Auraxium NS weapons.
■We plan on adding an advanced "prestige" directive tree to many of the existing directive trees that unlocks after you complete them. Example: You complete Heavy Assault so then you unlock the Stormtrooper tree that has much harder and less general things to do. That tree could of course have different rewards. In the case of the Heavy Assault it would probably be the ES Heavy Assault guns (Lasher/Jackhammer/MCG). In the case of Medic / Engineer we might look at the Medical applicator or Repair tool variants. We'd definitely get feedback from players on whether they wanted those sort of rewards though.
■The rewards are not currently account wide. Account wide stuff is tied into the marketplace so it was not as simple as setting a flag on the weapon (I looked into it). It's possible we could add support for that in the future if it becomes a popular request.
■We have discussed the next wave of directives, and we definitely want to add some for broad accomplishments, like overall kills, achieving battle ranks, and at least a few trees based on generic ribbon collector, like combat ribbons, support ribbons, objective ribbons, etc.
■We want more stuff like that, but there is a performance concern with adding a bunch of things of that nature. It's not hard to add them, but we're very careful about tracking all that stuff having a negative effect on server performance. That's why you don't see those currently.
We've thought of some ways around that though, such as having "Finesse" or "Acrobat" style directive trees that encompass similar feats that you don't just do once, but you can progressively get more challenging and fit better with the current style.