This is a really promising proposed trail that would lie to the west of the Great Divide Trail and include stretches in the Wasatch and the Arizona Trail.

The official Great Western Trail site has a map overview

The Wasatch-Cache National Forest section of the Great Western Trail (GWT) may be a good place to start. [archived link]

Notice the segments they list as NR (Not Recommended) - you would be pushing your bike up or walking next to your bike going down steep, rocky trails in many places on these segments. Segments 8 and 9 are the Wasatch Crest trail - one of the best mountain bike trails in Utah.

Farther south of segment 10 will be more steep terrain, but the GWT eventually makes it into American Fork Canyon and passes in front of Mount Timpanogos. This will be some tough trail in places, but there will be long parts you can ride. Then the GWT crosses Provo Canyon and goes up the South Fork of Provo Canyon, crosses over Windy Pass (another non-rideable section), then south across the front (west) of Provo Peak to Hobble Creek Canyon (rideable). Then I'm not sure where it goes from there, but it would be more mountain terrain.

Here are some more GWT maps (still not enough detail though)