I hope they can alias names elegantly. I really identify with some of my mains. Like my forum name has been my gaming name for like 20 years. So, that's a dealbreaker for me. I think Diablo 3 handled it well when they enabled crossplay. It's a complex problem, sure, but I'm sure they'll figure it out.
I logged in at 4AM PST the very first day, the very first minute, of Early Access to make sure I got the name I wanted for my Argonian character, "Sits-on-Dock-of-Bay." I'd most likely move on before giving that up.
"A probable impossibility is preferable to an improbable possibility." - Aristotle