Unlock all beards at lvl 10.
That will separate the boys from the men.
Since I really like the idea of showing your status through your characters' appearance, that idea seems quite good. Maybe a hat would be more universal for that matter and it's used already; I don't remember at which level but first you unlock a small elegant hat and then you unlock a top hat (hence very smart and subtle requirement, not sure if planned, in Gentlemen clan - because everyone has to wear a top hat).
I would also love (but that's just a dream I guess) some "show-off" items unlocked by having certain lvl in all classes. Like, when you have lvl 5, 10 and 15 in all classes you unlock some cool item.
Yep, leveling has been certainly a point of discussion, and what can be done with it, no one is really satisfied with the way it is atm, players or devs afaik. I think the plan currently is for an overhaul once Skirmish mode pops up.
Firstly, I guess you mean Adventure Mode (or more soon - co-op mode). I think the Devs told on the last chat that they want leveling not to be decided from achievements but rather from statistics (like those shown at the progress tab, for pilot it's kill to death ratio etc.). But even though the way you gain level may change I think the rewards won't, that's why I'm tackling this issue.