So there I was lying in bed trying to fall asleep when a terrifying thought crossed my mind.
What if this sale is CC's last hurrah for keycap making?
What if this is his way of giving all the people who supported him over the years one last chance at getting a Clack, and then poof! That's all there is there is no more. 
I've been thinking about this too.
On one hand, while this is the first public advent calendar, it seems like there's been sales like this before. In that sense, this would be another ordinary sale.
On the other hand, the whole clack thing started ~5 years ago. CC is an artist, and this skull design has been exhausted already--there's so many colors that already exist. I remember a multi-page debate on whether a clack was Chartreuse or Toxic because no one was able to tell the difference between two shades of green/yellow. The creativity in artists tells me that he's beyond bored making these skulls by now.
An even stronger sign lies in the FAQ describing why the whole CC thing started in the first place. He mentions bad health and trips to the hospital several years ago. Last year, he mentioned something about not being able to walk after taking a hiatus from clack sales.
bad health+overused design=???
oh btw grats Lurch!