A good (but already known) reason to leave gmail.
This only makes sense if you get a server at an off-shore host for mail, instead of using major email providers.
You speak of "off-shore" as though it represents some magically lawless region. As useful as that might be for these purposes, it doesn't exist. Your server will exist in some country. That country will have laws; those laws may or may not favor you. That country may or may not wish to refuse a US court order. Most countries are on fairly good terms with the US, and unlikely to say "no" to a request for evidence based on what looks like a standard legal investigation. Many of the countries not on good terms with the US rank pretty high on the list of places not well known for respecting rights, least of all privacy. And on top of all that, keeping a server outside the US does not render you personally immune to a US warrant if you remain in the US.
(Most of the above applies for s/US/$country/g as well.)
You're likely better off hosting a mail server here in the US, not actually storing any mail on it, downloading the mail immediately to a local mail store on an encrypted disk, and using encrypted email to protect new mails. That still won't render you immune to prosecution, but you might consider the consequences of refusing to decrypt a server preferable to the consequences of revealing the contents of your email. Or not.