Some of the newer tech studies indicate that, for the same capsule/vehicle size, the tubes have to be considerably bigger (approx 4M diameter IIRC) than originally envisioned by Musk. This is to prevent supersonic flow of the remaining air around the train.
Also, some who have looked at the idea question the ride quality. The biggest issue seems to be the alignment of the tubes: even if they are just 1/4" out of true "straight" (often tough/expensive to do in real world CE projects, given settling and seismic issues) that's going to be a very uncomfortable ride at 800 MPH. Jittery, bumpy, supersonic air screaming by, no windows, strong acceleration forces on start up, light/heavy in the seat as the tube varies in elevation over rivers, etc at 800 MPH --"Stand by to board the Vomit Comet Northbound to Frisco! Thirty minutes of fun. Just a few more minutes while we finish hosing out the cars, then we will board."
Maybe passengers aren't the best cargo for this thing. Freight has much lower safety and comfort criteria, can pay just as much on a per-pound basis, and has fewer ancillary issues (luggage handling, medical emergencies, etc.). And a Hyperloop freight terminal with links to surface/air transport would be much cheaper to build than a passenger terminal and could use land well outside of the expensive built-up urban areas. As freight pilots know, the best thing about that job is "boxes don't complain."
"Freedom begins when you tell Mrs. Grundy to go fly a kite." - R. Heinlein