FINALLY! NARP is announcing that effective May 1, 2017, there will be a Thruway connection between the Sunset Limited at Maricopa, and points closer to the Phoenix area. The bus will connect with Train 1/421 from points east and to Train 2/422 towards points east. For now there won't be a connection that would allow travel between California and the Phoenix area.
The bus will run Maricopa - Tempe - Phoenix Sky Harbor Airport - MetroCenter Mall. Note that it will NOT stop in downtown Phoenix. However, the stop at the airport allows one to take the airport's SkyTrain to the Valley Metro light rail. The stop in Tempe is at the former Amtrak station (from when the Sunset ran that way rather than via Maricopa), and is a block from Valley Metro's Mill/3rd light rail station in downtown Tempe. The bus stop at the MetroCenter Mall is currently not near any rail transit, however by 2023 or 2026 when the existing light rail line is extended to the same mall, it will be.
The Thruway bus connection from Train 1/421 at Maricopa will be 8901. The Thruway bus connection to Train 2/422 at Maricopa will be 8602.
The MetroCenter Mall and Phoenix Sky Harbor Airport Thruway stops are not new to Amtrak's map. The Thruway connections between the Southwest Chief at Flagstaff and the Phoenix area use the same stops.