However this really should be part of the RFC, or else anyone banning mixed names would be "non compliant". If the RCF does not specify this then the best that gmail (or any other system could do) would be to prevent people registering mixed names themselves and giving a warning (and maybe colour characters) if email is recieived from an address with mixed scripts.
Gmail, Microsoft and Yahoo and others like gmx, universities, big companies should simply refuse these mails. Microsoft should make Exchange so that this is the default way for handling these mails. The same goes for qmail, postfix etc. But that won't be enough.
As another commenter said, you can make up latin looking names using cyrillic characters, and we won't notice. How do you catch that? I guess this will the the time that PGP will prove it's value.