As I read it, BLW is promising some "future proofing" of capacity over the Cajon Pass as a way of mollifying the car lobby about taking "their median" that might have otherwise been used for express or managed lanes.
The future proofing is in 2 parts:
1) Dangling the option for a work-commuter oriented station at Hesperia to offset any worries about capacity over the pass. The ultimate park and ride, that would siphon drivers out in Hesperia rather than fight with them for capacity over the Cajon Pass.
2) Reassuring that they're still leaving generally room for 1 Express lane and sometimes +1 Managed Lane along most segments.
As I reckon from LV Strip to Cali:
LV Strip Station
to state border (34 miles)
07 Miles on East Side of I-15 until St Rose Parkway (straight North-South)
06 Miles in Median from St. Rose Pkwy through the Seven Magic Mountains area (a curve)
19 Miles on the east side of I-15 (alongside, not between, straight NE-SW) 
02 Miles in center median (lining up with Cali at state border)
---- NV - CA Border ---- (Border to VV 135 miles)
51 Miles from State Line to Baker (in median)
45 Miles from Baker to Barstow (in median)
39 Miles from Barstow to Victor Valley (in median)
(Exit 161 Dale Evans Pkwy)
50 Miles from Victor Valley to Rancho Cucamonga 
-- 08 miles from VV to downtown Victorville (in median)
-- 02 miles on viaduct through Victorville
-- 10 miles to potential Joshua St Station, Hesperia CA
(exit 141) (in median)
-- 04 miles to Cajon Pass (in median) (promise room for 1 express lane too)
-- 13 miles through Cajon Pass (promise room for 1 express lane too)
-- 13 miles Cajon Pass to RC (promise +1 Express Lane to Rt 210 +1 Managed Lane south of 210)
(final 3000' from I-15 to RC Metrolink via 3000' viaduct)
40 Miles from Rancho Cucamonga to LA Union Station (approx)
LA Union Station
Feel free to fact-check the above.
34 NV miles + 135 CA miles = 169 miles in BLW's map
50 Miles on I-15 between VV and RC implies BLW station at Exit 161 (Apple Valley)
 Some say 19 miles 17+2, some say 21 miles 19+2
 approx based on I-15 miles