To add, for me it would also be useful to schedule around the spring/summer equinoxes and summer/winter soltices as they move around.
More generally: it is useful to set event recurrence to align with another already created/imported event. So if soltices were to have been imported, I could create a new event and choose from drop-down menu 'same as "summer soltice"'.
I firmly second this suggestion.
To add, for me it would also be useful to schedule around the spring/summer equinoxes and summer/winter soltices as they move around.
More generally: it is useful to set event recurrence to align with another already created/imported event. So if soltices were to have been imported, I could create a new event and choose from drop-down menu 'same as "summer soltice"'.