Is there any hope of US adding service to SLC from the east coast hubs, either PHL or CLT?

It seems like of all the cities out west that have PHX-only service, SLC is by far the largest market. I appreciate that it is a captive city to DL but it is a huge hassle (and expense) to only have the option of flying to Phoenix in order to get to Utah.

Has US ever run east coast to SLC service in the past?