I really want to just stop here and ask you what you expect will happen if you take a multiplayer game with n players and increase it to have 10 times the player count (10n).

Do you expect bandwidth sent per-player will:

a) stay the same b) decrease c) increase

?

> Streaming sounds and FX every single time and never caching is a choice that will lead to 10Mbps

Nobody is suggesting streaming sounds and FX like this.

If it helps you, completely ignore my comment about sounds and FX. Focus instead on how the per-player bandwidth has scaled up, eerily close to 10mbps per-client, when you take any of the classic games you mentioned, and scale their player count up to 1000 players and see what happens.

> All you "really need" is initial state, the timestamps / inputs of the other players, and reproducible physics.

Yes, this approach works for low player count games, but as player counts increase the probability that you'll be stuck waiting for the most lagged player to deliver input to the server approaches 1.

So no, this is not all you really need. This approach doesn't work well for high player count games (I wouldn't use it for any game with more than 4 players personally).