I agree - I'd much prefer the "character@global" system that Cryptic moved to with their subsequent games. I played CO, STO and NW and never had any issue with bumping into players with the same character name (or ship name in the case of STO). I'd probably find it funny in fact.
It's probably not impossible to do - but then it would just be a matter of how difficult and time-consuming it would be to navigate that spaghetti. Kind of like the power FX changes (and other features implemented during live) - it was "impossible" until the devs decided they could spare the time and manpower it would take to re-work the powers system.
I'd LOVE to see them implement a non-unique name system like Champions has. That said - I'm not sure how possible it is with the CoH code. It might be possible with SEGS where they are building things from the ground up, and the various successors, as far as I am aware, are going with non-unique character names as well.