There are certainly a lot of questions about whether rail will attain its expected ridership.  For example, the projection of 15,000 riders who would walk to rail seems to be quite an overstatement.  The current route from Kapolei to Pearl City goes through lots of light industrial areas, open space, commercial areas, and farmland.  There's relatively little housing there.  Maybe in 50 years conditions might change, but as of now, people would have to walk very long distances in order for rail to attain that 15,000 number.  The dearth of housing along the rail route is evident in this video of a flyover over the rail route:
https://www.youtube.com/watch?v=PYu2C3tDWBI