@marlowe1 and @JBStillFlying - you raise interesting points, but the data we have doesn’t seem to support it. Of most import, the AO company line seems to be between 4-5k ED apps. I doubt they’d be short-selling for any discernible reason here.
Also, while JB balks at EA apps being much over 11k, keep in mind just 4 years ago, Chicago was pulling 12k EA apps: https://www.chicagomaroon.com/2016/05/31/university-admits-record-low-7-9-percent-to-class-of-2020/
Finally, while the assertion that Chicago is a singular (more niche) flavor is interesting, here, I think sheer popularity outweighs individuality. The glitz and glamour of Brown and Columbia (while maybe not singular - places like Wesleyan and NYU often serve as backups to these schools) prove more alluring than a place that is singular, but grittier (like Chicago).
Remember, we’re talking ED, not EA. Sure, as seen in 2016, lots of students are willing to make non-binding commitments to Chicago. But, the “niche/grind” schools, like, say, Hopkins, tend to attract fewer apps than the more glamorous options for ED. (Hopkins gets around 3-4k early apps.) I think Hopkins is a good comparator here.
I think, per all the discussion here, generally more particular students are ready to commit to Chicago, and they certainly don’t exist in higher quantities than the types found at Brown or Columbia.
After all, if you like Chicago but are reluctant to commit completely to such a particular place, why not just apply EA?
That’s why, along with what the AO says, I’d be very surprised if ED apps were north of 5K. (Heck even Harvard and Yale only get 6k ED apps, and they have two of the biggest pulls, probably domestically and internationally.)