As a frequent visitor to the Ketchum/Sun Valley area by both air and automobile, I have several observations concerning the proposed new airport being suggested at some point south of Hailey and Bellevue.
First, it takes a minimum of one and a half hours on a good day (meaning not having to follow a truck or slow-moving motor home) to drive from I-84 to Ketchum/Sun Valley, and that is maintaining all the speed limits, even the posted 25 mph through Bellevue and Hailey.
Second, I have also experienced trying to fly the last link from Salt Lake City to Hailey and having the Hailey airport socked in, which required landing in Twin Falls and riding a bus to Ketchum.
This all leads up to my suggestion, which is to keep the current airport in Hailey as is and build high-speed rail service from the Twin Falls airport to Ketchum and Sun Valley with necessary stops in towns along the way. Such a rail service would cut down on automobile traffic (and subsequent pollution) and could provide a relaxing and quick way to get from Twin to Ketchum/Sun Valley. And, even with stops, it could be faster than driving 25 mph through Bellevue/Hailey. Finally, it probably wouldn't cost much more than a new airport, albeit I have no idea on this count.
Even with a new airport someplace down valley, I would suggest that a new road would need to be built bypassing the aforementioned towns so that traffic could move at a reasonable pace and Hailey and Bellevue could continue to dwell in peace.