"Fall 2019" in Chicago means September or October (literal) at the earliest. Based on living there for 2 years recently, it's just as likely to be early 2020.

Also, a functioning ATS means you still have to reclear security as it's not an airside transfer. Having to reclear TSA at Terminal 5 is less than ideal and likely negates any benefit over the airside bus that runs every 30 minutes.