You may soon be able to "link your [Android] devices" signed into the same Google account together. This will enable "call switching", which lets you switch between devices for calls, as well as "Internet sharing"!

A new "Link Your Devices" menu will appear under Settings > Google > Devices & sharing once this rolls out. The call switching feature might be using the new Telecom Jetpack library that I previously talked about.

H/T @nailsad_eleos