Maybe it is an API. Maybe the kernel implements this API and it can be called locally or remotely. Maybe someone invents an OAuth translation layer to UIDs. The API allows syscalls or process invocation. Output is returned in response payload (ofc we have a stream shape too).
Maybe in the future your “terminal” is an app that wraps this API, authenticates you to the server with OAuth, and can take whatever shape pleases you- REPL, TUI, browser-ish, DOOM- like (shoot the enemy corresponding to the syscall you want to make), whatever floats your boat.
Heresy warning. Maybe the inputs and outputs don’t look anything like CLI or stdio text. Maybe we move on from 1000-different DSLs (each CLI’s unique input parameters and output formats) and make inputs and outputs object shaped. Maybe we make the available set of objects, methods and schemas discoverable in the terminal API.
Terminals aren’t a thing of the 80s; they’re a thing of the early 70s when somebody came up with a clever hack to take a mostly dumb device with a CRT and keyboard and hook it to a serial port on a mainframe.
Nowadays we don’t need that at all; old-timers like me like it because it’s familiar but it’s all legacy invented for a world that is no longer relevant. Even boot environments can do better than terminals today.