I'd go with Easy Rhino.
Now who here gets that reference?
With my friends it makes it easier identifying them by their username. but then none of friends are called "CB0008675dddbyyt56633vnjasio" They have good reasonable names (We are all members of the 501st too, so we generally use the names we use there). That said, I agree that callsigns would be a cool addition, something like how they work in Ace Combat 7, were you unlock in-universe callsigns.
However again, I can seea problem with even this, in that multiple people may want to same name, that could be fixed by having a list of preferred names and the game assigns from that.
However simple squad number names such as Red Leader, Gold 4, Obsidian One and so forth,would be the best way to go. All you have to remember is their number. That said, for the display purpose I think a mix of Username under call sign should be the way to go.
Example:
Red 2
The_Hopfot
Or
Nerf Herder
The_Hopfot
