I would love to see more options for rebranding right from within the admin panel.
Things like:
Add logo
Add website/app icon
Pick a Google font (or two).
Add custom CSS
Yes! This is what I want as well! We have some cool plans about the UI and rebranding options but we have to wait for 4-5 months for these features. Currently, we are focused on improving email campaign analytics, segmentation and more targeting options.