Missouri/Illinois
Some road fans want to extend I-72 in both directions. First, a westward extension is envisioned for I-72 across Missouri and Kansas, eventually going into Colorado. This would provide an alternative to Interstates 70 and 80. It would also relieve traffic on the latter route between Omaha and Chicago, and on the former route between Denver and St. Louis.
An eastward extension would multiplex I-72 with I-74 for some time, loop it around Columbus, OH and end in Pittsburgh.