You should be able to send marketing emails to the secondary email address field. We market primarily to couples who each have their own email address but are really one customer. As it stands now, you can only send marketing emails like newsletters to one address so the spouse does not receive it.
Thanks for your comments on the idea. This isn't planned for development in the next quarter. For transparency and clarity, I'm updating this issue to 'Not currently planned' for the time being. We will re-evaluate in the future and we will update this idea if anything changes. Please feel free to upvote and continue to leave feedback on this thread.