There is a reason I liked the old (1.5 and below) launch system; it make it trivial to write a shell script launcher that would let you play your client in offline mode.
As a server admin, I could use it to log in as users, and fix their situations.
As a video recorder, I did use it to log in as "CameraMan" to record someone else on a server without disturbing "Keybounce" on that same server.
Some people, for some reason I've never understood, think that if I'm talking about launching in offline mode, I must be talking about stealing the game.
1.6 and above? It's a complete pain, and I don't have it working. I did request that on MultiMC, and they said it would go in, but I don't know if it is in yet or not; I strongly suspect that if Microsoft does anything with the login servers then it will be in MMC very very quickly.
Now, I do have one issue. I have a creative mode test world, that has normally been used in 164. I just used it in 1.8, to test the new vision system, and then ... all the player information had been changed to UUID form, and no longer usable by 164 clients. That's a real PITA. This on a server that runs in offline mode. So ... yea, even offline servers talk to the mojang servers.