I wouldn't do it. Here is an example: there is such email provider is fastmail.fm (recently bought Opera). He has a lot of domains (fastmail.fm realemail.com, mailc.com etc.). To some point all these domains were aliases. That is, emails sent to firstname.lastname@example.org, email@example.com, firstname.lastname@example.org got the result in the same drawer. But one prekrasny the time (sometime in 2005) Fastmail decided to "share" a domain with all its consequences. It was a lot of confusion. You can't predpolagat that if 2 domain aliases today, they will remain the aliases tomorrow.
There is one caveat: on some standard emails sent to email@example.com and firstname.lastname@example.org fall in certain cases in the same mailbox. This trick works with gmail but not works with most other email providers (which do not support this strange RFC). What will you do in this case? After all, it's not even clear which providers support this.
P. S. Add to your list of aliases: aol.com and aim.com aliases from the point of view email (email sent to email@example.com and firstname.lastname@example.org falls into the same mailbox).