Currently, the long term proposition is to extend Idaho 16 south to I-84 (construction likely to begin the next couple years), and then north through Indian Valley to a point somewhere south of Council on US-95, built as an expressway. That northern extension has met considerable opposition- there have been many, many articles written about it and I think there's information about it on the ITD website. I don't have time to look now since I'm at work, but I could probably pull some stuff up when i get home tonight.
The Council->Whitebird segment would be hugely difficult to turn into freeway without major realignment or destruction of the river- they'd have to do something quasi-similar to I-70 in Colorado, and Idaho just can't afford to consider that at this point.
On a cultural note, a freeway connecting the two sides of the state would be huge. 95 gets down to 45 MPH for several miles between New Meadows and Riggins, and the road has the be repaved every few years because it gets warn down by trucks to no end.
From a cultural standpoint, the two halves of the state are well separated, since US 95 is literally the ONLY road connecting them, so it would be nice to see a better road through there, but that's a long way off