I'm a security expert and would love to take up that challenge - but then I have access to internal tools and can tell you the answer
I can guarantee however that your email address is used on multiple sites. We don't control the security of 'all the sites' and as a result whenever another site that is using email address is hacked and your details disclosed, that the attacker will know who to phish or similar. Not so true for a Display Name that most people don't always get to use on every site they visit...
Not everything you think is 'hidden' truly is.
So you know, that the mail of my own domain is not exclusively used ? When I own several mail-accounts that are exclusively under my own control ?
Respect... but I would suggest, that you are a little less bold on what you claim to be able to guarantee.
And even if I did use my email-address on any other site, then someone would still need to figure out, that I am using that e-mail for SWTOR too... With your proposed new system, noone needs to take any guesses. Everyone interested in hacking will know for sure, what my login name is.