It sure would be nice add the seasonal equinoxes and the solstices to the yearly holiday list so that they would be displayed in the module. It would be a nice way to highlight the seasonal categories.
 
By the way this Sunday is the First Day of Spring - for those who are astronomers it's the Spring Equinox.  

Generally, on GCU the link that you provided is identified as a category. I mean the Holiday List module that displays the upcoming holidays. It is an optional part of the store layout and content.
 
The list identifies all the holidays up to the year of 2015. http://www.greetingcarduniverse.com/holidays/
 
I was surprised to see that all of the seasons are missing from the list. They have Nurse's Day listed but not the 1st Day of Spring. Out of all the holidays it is the most scientific and I'm sad to see it not on the list.
 
It would be a great way to feature the seasonal cards and it doesn't have to be the religious cards (pagan etc..) There are seasonal party invitations, and seasonal occasions categories as well.