The question is about density and whether that's something to pursue even if it's prosperous.

It's an incongruous question. Hyperloops between Basel, Bern and Zurich would make them into one virtual Mini-City. The loops would also reduce density in the travel corridors preventing a California catastrophe kind of sprawl inbetween.

On the mountains that the hyperloop would traverse? ok dudes

Basel<>Bern (direct) would need tunnels.. The other 2 routes are pretty flat. Most of the Swiss economy is in the valley between the Jura range and the Alps.

The necessary tunnels for Basel would probably cost less than this:

https://en.wikipedia.org/wiki/Gotthard_Base_Tunnel

But Bern<>Zurich is the SBB's bottleneck.