New Interstate designations, even for uncontroversial already-built freeway corridors, have long been low on Caltrans' priority list. CA 15 and CA 905 also languish in the potential Interstate designation queue.
Isn't CA 15 still waiting on some upgrades to bring it fully to Interstate standards?
How about VA-895, VA-288 and VA-164? I provided pages of advocacy documentation 2 years ago to VDOT upper management about getting these incorporated into the Interstate system, and they weren't interested, even claimed that the first two are not built to full Interstate standards, which I disputed using AASHTO documents.
They did make the valid statement that there would be higher internal as well as FHWA responsibilities and policies associated having a route in a higher system. More to it than just replacing the route signs. Still, get it done and it is done once and for all.