JSTARS is a real antique. As long as we plan to continue to put a manned system up for enemies to shoot down, the most logical choice, IMHO, would be to move the electronics suite into a larger, newer civilian airframe. It’s not like there aren’t plenty of newer airliners around.
There was a plan for that on a 767. I think it was going to be called an E-10. Don’t know what happened to that initiative. I am sure it is DOA while Obama is in office. You can bet that there won’t be any movement on it while next generation tanker saga drags on.