Well, 1st, the Mococo's current name on the UP these days is the "Tracy Subdivision" and extends from Lathrop to Martinez.
2nd, it is much cheaper to take an existing line and fix it up than it would be to put track back in over Altamont.
I don't think you will see new track placed back in on old SP right of way over Altamont, at least not in my lifetime. At the time SP track over Altamont was taken out, business was drying up and as a condition of the UP-WP-MP merger that happened on December 22, 1982, SP won trackage rights over the adjacent UP line that is currently called the Oakland Subdivision. As far as the people that haved moved next to the Tracy Subdivision next to the portions that have been inactive, well, they should have got it in their mind that if the railroad still owned the property, that it could possibly be used again at a much later time for future use and the residents would have to "adjust" accordingly. I had to laugh a couple of years ago when I read a newspaper article, quoting some executive type woman who worked for BART that bragged away about how the UP would just fall to the ground to sell this line to anyone who wanted it, including BART. I have news right back to this woman, that UP learned their lesson years ago, that if there is a through, secondary route, especially if it conncets with either, other UP lines or other major railroads, never to give it up, or if you do, you will screw yourself. I knew several officials on the old SP who are now retired that said in the early 1990s that SP wished they still had Altamont Pass and for another example, the old South Line that ran from Benson Arizona to Anapra New Mexico. In the case of the South Line no longer existing,(at least east of Bizbee) SP, now UP, to increase capacity had no choice but to add a 2nd main line to the North Line (now Lordsburg Subdivision) between these 2 points. It is cheaper anyway because the South Line no longer exists. I almost bet that if the South Line still existed today, UP would have fixed it up and would be doing directional running with it.