Dec. 15th, 2019 is a Sunday and typically decisions are not released on weekends. What would an anticipated decision date be?
It won’t be 12/13 for sure as that would seem inappropriate and only someone with a bad sense of humor would choose that date.
From past trends, ED/ED1 has always been the first Friday in December. So 12/6 seems reasonable, if a bit early.
For class of 2021, it was Thursday, December 14.
If it was the WashU graduating class of 2021 it was 12/9.
Oops! You are right! Class of 2022 was 12/14!
My other son is class of 2021 – hard to keep the years straight sometimes! 
ED1 Class of 2023 Decisions came out December 13. In recent years, they have been released on a Thursday afternoon. My guess is Class of 2024 will be released on December 12.
ED/ED1 decisions are always announced sometime during the reading period (week before finals). 12/9 for Class of 2021 was kind of early, so my 12/6 guess for this year is optimistic.
I don’t know if it’s a coincidence, but for the last few years, WashU ED decisions were announced a couple of days after Cornell’s ED announcements. Maybe checking the Cornell threads might help in analyzing the tea leaves.
Class of 2018 was also 12/9, which was a Monday that year.
Definitely looks like next week. 12/12 seems to be a reasonable date, since that is the first day of finals at WUSTL IIRC and things should be relatively quiet.
Cornell comes out on the 12th. I wonder if that means anything