The Iowa DOT has a “corridor preservation plan” out for a road northwest of Oskaloosa, running from IA 163 to US 63. This step in making a bypass seems, to me, like a relatively recent thing, but I could be wrong and/or didn’t see notices years ago.
The map (PDF) shows a general southwest inclination starting a few miles north of Oskaloosa, but then the corridor takes a sharp turn west to a larger preservation area that would include a future interchange. This will mean that 63 will exit from the existing four-lane — exiting from itself, so to speak — in a weird way. It also raises the question of how mile-marking will change between this point and the current 63/163 split south of Oskaloosa, which just so happens to be Exit 60 in both directions.
A look at the satellite view makes me wonder why they can’t put the interchange closer to Kirby Avenue, which would cut down the out-of-the-way-ness of that southernmost part of the bypass. That’s where 163 deviates from the original path into Oskaloosa straight south, making a seemingly ideal place for a trumpet interchange and a place where northbound 63 could go relatively “straight ahead”.
For what it’s worth, the bypass will create the westernmost point of US 63 north of the Arkansas/Louisiana state line, replacing the current point, which is just north of where the bypass is expected to rejoin current 63.