I don’t really have a preference on the question of evergreen or not, but would like to point out that you don’t really need to be restricted to ‘7 topics’. You could easily do 14 topics and repeat them every 2 weeks instead of each week.
The FStoppers community also runs regular challenges (called ‘contests’) and they have many different and specific themes. Sadly, though there’s lots of back-patting, there isn’t much education going on. People seldom say how they captured something, or how much they processed it.