This might be a dumb question, but why do terminals spew output anyhow? Past a certain point it's clearly unreadable. Once the terminal starts getting behind this is a UI failure IMO.
So why not (say) buffer it up somewhere, show a preview, show a "I would be spewing output right now, press <Space> to see what the last screen is, press Ctrl-C to stop, press 's' to just spew output". The speeds and amounts of data for which this happens could be completely configurable.
You can always put a limit on how much to buffer up (I'm not saying that this system should completely buffer output files until you run out of disk space), and sometimes 'spewing' is actually what we want.
The vt220 had a 'slow scroll' speed which would buffer text and scroll it at a viewable speed, limited by the quite small memory on the screen. It also had a 'pause' key which would pause the display and then continue the output (again limited by the terminal's memory). See also PC 'scroll lock' key.
The way to tackle this is not to "buffer output up". In fact, the way to tackle this is the opposite of filling up buffers with output.
It is to decouple the terminal emulation from the rendering. Mosh runs the terminal emulator on the remote server machine, and transmits snapshots of state (using a difference algorithm for efficiency) at regular intervals over the network to the client, which renders the terminal state snapshots to the display on the local client.
Various tools can and do deal with the spew though. Ofhand, script (typescript), screen, and tmux. If you're running a session through a serial terminal emulator (e.g., minicom), that would be another instance.
I'm not going to claim these are particularly mainstream uses (though I've made use of each of them, and been grateful for the ability to do so). But they do exist, and I suspect there are others.
So why not (say) buffer it up somewhere, show a preview, show a "I would be spewing output right now, press <Space> to see what the last screen is, press Ctrl-C to stop, press 's' to just spew output". The speeds and amounts of data for which this happens could be completely configurable.
You can always put a limit on how much to buffer up (I'm not saying that this system should completely buffer output files until you run out of disk space), and sometimes 'spewing' is actually what we want.