Could future versions work in buildings? What’s the issue there? Just that it’s father away than a cell tower is?

Starlink signals are essentially line of sight right now. The bump up in power to penetrate even a single layer of drywall is almost certainly way outside the power budget of a Starlink satellite.

Whether a material is opaque to it. Buildings are transparent to lower frequency radio. Imagine that the satellites transmitted in visible light, doesnt really matter how powerful it is if you're in a room with no windows.