Which Gmail APIs? Has there been an update to IMAP that I'm not aware of?
By the way - the IETF standardised an OAuth2 SASL mechanism (RFC 7628) a couple of years ago, no idea why GMail doesn't support it.
Basically, the only thing that is kind-of Gmail specific is the auth support (https://bugzilla.mozilla.org/show_bug.cgi?id=849540). If Gmail sometimes in future switches from OAuth2 to some other protocol, the client will have to be updated.