It would be great to have the ability to use a custom email template for our newsletters.
Something along the lines of how we create page designs in themes so a file along the lines of newsletter.hbs
This would be great for keeping the newsletters inline with a themes style guide.
Agreed. I was searching through the source code today looking for something like this.
Yes, more specifically, it would be great to have control over fonts, colors, the ability to preview the newsletter appearance and customize it for light/dark mode, and also to customize the way that the email-only sections appear (I wish I could color them/style them to be more separate from the body of the newsletter, like a call-out box.)
Yielding the control to the theme designer would likely be the simplest fix and be great for consistency in branding.