The USAF dropped the JSTARS replacement because it was becoming too vulnerable to modern air defences. But wouldn’t the same problem apply to other recce platforms like Global Hawk, Rivet Joint and Sentinel?
I wrote this story for the Paris Air Show coverage by Aviation International News (AIN). You can find it here:
https://www.ainonline.com/aviation-news/defense/2019-06-15/does-jstars-demise-spell-end-airborne-isr
Addendum, August 2019: I just noticed this USAF Air University paper from 1999 discussing and predicting the migration of AWACS and JSTARS into space. As the old adage goes, there’s nothing new under the sun! Moving AWACS and JSTARS missions into Space AU thesis Oct99
Chris Pocock Makes Aerosense 