Since Kagi is a paid search, it would be nice to have a very basic "start page" that we could set our browser to. This would allow people to have a few pre-set links to websites/apps that we use. Also, maybe have local time and weather on the page.
Think of a new tab type page, with some shortcuts to favorites websites, and maybe weather.
To make this fit along with the Kagi theming, keep it simple, with perhaps a row where paid users could add/manage/use favorites. Also add where they could have the current local weather / time.
This would keep things simple and lightweight on the Kagi side and also, being only a paid feature, could potentially be a draw for new customers.
With the existing ability for custom theming through CSS, Kagi would not need to add all kinds of crazy theming tools.