True, but that means you're going to have some absolutely awesome bearing system that gives almost zero friction along the major axis of the pipe while also giving almost zero slop in the other axis. Which is damned hard. Adaptive maglev bearings maybe? ;-)
Why do you want zero friction along the major axis? Linear speed of pipe movement through the bearing would be very low: not more than couple hundred feet per day. And what do you mean by zero slop?
By the way, if you want to continue speculating on Hyperloop thermal expansion issue, you can join my speculations - I wrote a few comments under this blog post:
Tubes are fixed to the pylons, just not rigidly (in longitudinal direction).