So this is probably not the right thread for this, but since you all are talking about it anyway...
Here's a crazy idea: how about overhauling the entire designation system to something that logically makes sense and is garrison based, instead of costume based? Every new member would still receive a chronological, numerically based designation, but they'd have alphabetical designations to identify which detachment and garrison they're with.
Bear with me here...
For example, John Doe just signed up for the 501st, so he would receive the next available numerical designation of "12345" since he's the 12,345th person to join. Now, because he lives in Brazil, and within the boundaries of the Brazilian Division Garrison, he'd receive the prefix of "BZ." Since he's wanting to be a Snowtrooper, he'll receive the alpha-numeric suffix of "T3" (where T is for Trooper, and 3 is for the Snowtrooper variant). So when all is said and done, John Doe's daily designation would be "BZ-12345 (T3)." For daily trooping use, he could just go by "BZ-12345" or if we really wanted to keep it more in line with the movies, just use the last 4 digits and go by "BZ-2345." Chances of another "BZ-2345" ever existing are astronomically slim. Oh, and as for heritage troopers with only a three number designation, they'll get to keep those.
What about outposts? Well, same rules apply. Jane Doe from Romania wants to be a Dark Side Force user, so she'll receive the designation "RNO-12346 (D2)," where "RNO" represents the Romanian Outpost, and "D2" represents Dark Side users.
Basically, all Garrisons would get a two character alphabetic designation, whereas Outposts get a three character one. And the T=Trooper and D=Dark Sider thing is just a placeholder. I think it'd make more sense if the costumes were reworked to be associated with A, B, C, D, etc, so that you can have Trooper equal something like "A," since Troopers were the first costume to be inducted, and any trooper variant would be a derivative, such as A1, A2, A3, etc.
Hope that all kinda makes sense. It'd be a pain to iron out all the details, yes, and I'm sure a lot of the older folks will be resistant to change, but it'd be a far more logical system for the designations, and would keep the "TK" envy at bay. It would also help set up for the future in that any new costumes would just be given an alpha-numeric designation, and put into a categorical subset, depending on what they are.
Thoughts? Hope that all kinda makes sense.