1,000 km/hr is over 600 mph, while the fastest public bullet train in operation is the Shanghai Maglev @ 268 mph. Big diff'.
As for g-forces, they are related to acceleration & not to speed. So as long as the FluxJet folks can figure out how to get up to max speed & slow down to stop at small rates and minimize/eliminate turning (all significant limitations), there's a chance neither obese nor skinny passengers will suffer.
This recent American Bazaar article notes that Musk's plan for a San Francisco-L.A. hyperloop proposes a limit of no more than 0.5 g's, while
this earlier PBS News Hour piece cites plans to mimic the 0.1 to 0.3 g acceleration of a commercial aircraft on takeoff.
My head is slowly beginning to wrap around the technical points of this extreme travel thing, but I don't expect to see any of these public transport options operating in my remaining lifetime. And I'm OK with that, because I've never liked rollercoasters either.