When I hover over a link when not using reader mode, it shows me the address of the link in the bottom left of the browser window. This does not happen when using reader mode. This feature within reader mode would serve the same function as it does outside of reader mode: enabling the user to see the actual url hidden behind a link.
This feature would be useful to prevent bad actors disguising a particular url behind a misleading link. Beyond the obvious security benefit, it would extend all of the other ux enhancements that this feature provides to also be present in reader mode.