You still routing outside to your channel peers, no? You also set the prices for your channels, It would be nice but still it ain't purely "localhost" style, tbh... 
--allow_self_payment, --outgoing_chan_id  --last_hop and --fee_limit are your friends but still....

JesseJames

south_korea_ln

This wouldn't be implemented as a protocol thing, so no channels involved.

I just want to do the equivalent of accessing localhost without requiring access to the internet but lightning requires _real_ channels and _real_ routes for _every_ payment—no exceptions.

lightning

We're so early, LND doesn't even support loopback

Wait, how would this work?
You'd have to bring funds from one of your channels into another one without going through a peer, no? This would require some onchain swapping? Or at least, increasing the size of one of the channels? I'm probably missing sth there...