Thanks for reaching out! The developers have included some fixes to known issues with the gateways; however, the core functionality has not changed. Outgoing Gateways in SmarterMail 16.x do not apply to local deliveries.
That said, this functionality could be considered for implementation in a future version of SmarterMail. I'm going to change this thread from a Question to a Proposed Idea in order to facilitate tracking on its request. I'm also going to move this thread from the SmarterMail 16.x BETA category and into the standard SmarterMail category so it's not lost when we close down the BETA threads.