What an elegant client-as-terminal I have for this incredibly popular physics simulation! Oh no! it takes up too much bandwidth. Welp - time to throw out the old lock-step game-loop architecture, and allow each client to stream incremental updates
I'm sure many contemporary engineers had similar problems, and considered the same approach, but either shrank-from or gave-up on rustling together an elegant solution. Like many problems in the early days of 3d/internet gaming, Carmack seems to have rapidly and nicely solved it with imagination & experimentation, all informed by a broad and deep understanding of data structures, & algorithms, and presumably an industry-leading amount of experience.