My understanding is that the guy running gg actually tried it, and found it did not work. Partly down to email clients, but annoyingly, whilst a top level domain can have an MX record, it is actually part of the RFC that disallows this.
RFC2822 makes domain :-
Domain = (sub-domain 1*("." sub-domain)) / address-literal
But the older RFC822 made it :-
domain = sub-domain *("." sub-domain)
So it used to allow a domain with no dots in it, but now requires dots.
Shame, especially for many of those applying for new TLDs as they cannot have things like info@google as an email address.
Update: See comments as it seems I missed something and such email addresses are valid, just unlikely to work.