The cost and logic of rebuilding something as steep as Boylston Hill isn't too far fetched when you remember why they rebuilt Stampede. And the fact that (if I remember correctly without fetching and flipping through the grade profiles) Stampede has maximum grades every bit as steep as Boylston (and plenty of curvature to boot) means that the horsepower and tonnage configurations required to tackle Boylston would be little or no different from those already running over Stampede. Yes, the current route via Pasco is easier in terms of grade, but it's considerably longer, and much of that extra length involves slow running through the Tri Cities terminal area and Yakima River Canyon. It's my humble guess that any loss of speed crossing the Saddle Mtns. would be compensated by the savings in time and congestion elsewhere. Remember, they already send loaded coal and grain west down the Columbia while some of those empties come back via Stampede or even Stevens. So while some trains are routed by shortest distance to destination, others are forced by their weight to be routed by easiest gradient to destination. BNSF adding a new connection between Lind and Ellensburg would just be a sensible (if costly) expansion of their existing multi-directional Northwest network, gaining fluidity where they can. It's either that or carve enough new right of way to doubletrack major areas of the current Columbia River, Stampede, and Stevens Pass routes, and there are too many physical and environmental obstacles to do much more of that.