http://www.sltrib.com/news/ci_13479885 (http://www.sltrib.com/news/ci_13479885)
Meaghan and I took US 6 back in 2005 (http://www.ajfroggie.com/roadpics/ut/us006/index.html). Some of those canyon stretches look like pretty tight confines, and I didn't think UDOT would be able to upgrade them without "taking down the mountain". But it looks like they plan to do just that...
Only tight spot is near Price (there's some mining-like operation on the north side of the road. but, if they're willing to skim down on shoulders in that spot, four lanes should fit fine without any additional work. They've slowly been working on it since I first drove it back in 2005 (as well). What will be nice is if they finish it with a nice interchange at I-15.
Sykotyk
Well, I've heard plans to make US-6/191 from I-70 to at least Price 4-lane, divided. Add in the Price bypass and you might be able to make US-6 all freeway (or something awfully close) to I-15. Maybe this I-72 in Utah isn't so far off, after all.
I do agree, however, that Spanish Fork Canyon and Price Canyon would be the toughest parts to build a freeway through, and may be a while off.