I wouldn't rule out talk on extending the EOE westward picking up around 2025 when the current improvement program wraps up, especially if the IL 53 extension dies out.
I bet you it will be needed within the next decade or two. A link from Elgin to O'Hare without the use of I-90, and a nice in-between highway corridor between I-90 and I-88 serving the West/Northwest suburbs
I believe the western extension of IL-390 to North Ave/Lake Street will be an IDOT project, since it will be an arterial rather than a freeway. So ISTHA won't have anything to do with it.
I do wonder how they will get traffic to slow down between the existing western terminus of IL-390 and County Farm Road if the CFR intersection will be a stoplight. There does not seem to be a lot of space between the roads.
IL-390/US-20 was designed to have CFR go over it with a urban style exit layout. That is why IDOT didn't amass any excess dirt at the end like they typically do. The plan was to trench 2 ponds on each side of CFR to supply fill for the rise over. If and when they decide to extend it, they will probably use the same idea. Since the ROW west of CFR is wetlands, there are several more drainage ponds that will be trenched to supply fill as the ROW turns NW back to the original US20.
As you can see IDOT not having any money was a killer when the parcel in black was sold to the local school district.

I don't believe there was ever a plan to buy that property. The EOE was suppose to follow the existing US 20 west of North Ave, and it wasn't going to be full access control, more of a parkway-style with a mixture of at-grades and grade separations.
Yes, in the FAP-6 Environmental Review Report, there are notes about a meeting with the City of Bartlett officials on the extension of Bartlett Road south of the current US20 and work an intersection with Oak Street (now Oak Lane) due to a high accident rate at Oak Street (Lane) and US 20. There were also concerns that the then Eastview Junior High (now Bartlett Middle School) was going to be too close to the ROW even though there were no frontage roads planned. They had already decided a cloverleaf was impractical and a diamond would have to be used.
This was in 1971/1972. When Eastview was expanded north by the Bartlett School District in the 1980's, they took up the buffer space the ROW expected to acquire and today IDOT would have to condemn all the retail property between the school and US20 to make it work.
Here is a closer view of the Elgin-O'Hare/Bartlett Road Exit was supposed to look like.
The light blue is the ROW
The green line is IDOT owned property
The purple lines are proposed water retention ponds
The redline was the proposed Bartlett Road to Oak Lane extension with the diamond ramps.
It also shows how Oak Lane was going to dead end into a circle drive for the school and north of the EOH it would be a service road for the retail strip center.
The dotted light yellow shows what happened when the school expanded north.
The EOH was supposed to go below grade between US20 on the right all the way past the school to keep road noise down and then rise as it meets Bartlett Road and then move north back to the current US20 alignment.

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You can even see where IDOT bought land from the developer across Oak Lane from the Junior High. The grading for the streets and cul-de-sac are still visible.