Motivation
See parent T325238: [Epic] IP Address Reveal for Privileged Users for details.
Proposed mockup
There would be a "show IP" option in each record in Special:Contributions which would reveal to show the IP address in place for each revision/action.
If the IP is no longer in the database, it is replaced by "unavailable".
Testing notes
This can be tested on Special:Contributions for a temporary account on beta or locally.