Nevermind that you failed to be consistent in tag values between logging schemas... nothing in this proposal addresses the reason that I myself had implemented mod_remoteip, which was authn/authz control. In the limited scenario you have considered, authn is pretty much a noop on the physical address (no public client would ever be routable to that server anyways) so access control is shifted to the consumer of the web resources.
This patch would have a long way to go before being considered... and is certainly not a 2.4.x candidate. The very design of mod_remoteip keeps the precious values that you are concerned about losing as request notes suitable for logging. But Stefan also points out some flaws in the current approach. The correction is simple; promote the remote_ip up to the request rec and log/use for authentication that r->remote_ip throughout httpd. Introduce a wire client logging tag for c->remote_ip.
