>One thing that's nearly impossible to replicate on modern systems is the extremely tight feedback loop these TUIs

Why? Yes, VSCode is slow. But Zed and many neovim GUIs are extremely responsive. Why would achieving that even be impossible or even that hard? You "just" need software which is fast enough to render the correct output the frame after the input. In an age where gaming is already extremely latency sensitive, why would having a text editor with similar latency performance be so hard?

Do you have any actual evidence that zed or neovide are suffering from latency problems? And why would putting a terminal in the middle help in any way in reducing that latency?

I'm not sure if you know what "terminal" means. I'm not talking about terminal emulators (the "terminal" program on macOS/Linux/Android/etc.) but actual, real terminals. The "terminal" is a text mode rendering mechanism built into computers of the terminal era. The closest modern operating systems come to it is the terminal-like environment you can get on Linux or the *BSDs by disabling the GUI, but even those merely emulate text mode, they still contain the stacks upon stacks of timers and necessary to process input peripherals.

The problem is the entire software stack between the keyboard and the display. From USB polling to driver loops and GPU callbacks, the entire software stack has become incredibly asynchronous, making it trivial for computers to miss a frame boundary. Compared to DOS or similar environments, where applications basically took control over the entire CPU and whatever peripherals it knew to access, there are millions of small points where inefficiencies can creep in. Compare that to the hardware interrupts and basic processor I/O earlier generations of computers used, where entered keys were in a CPU buffer before the operating system even knew what was happening.

VSCode isn't even that slow, really. I don't find it to be any slower than Zed, for instance. Given the technology stack underneath VSCode, that's an impressive feat by the Microsoft programmers. But the kind of performance TUI programs of yore got for free just isn't available to user space applications anymore without digging into low-level input APIs and writing custom GPU shaders.

In small part, CRTs running at 70Hz or 85Hz back in the mid-80s, as well as the much smoother display output of CRTs versus even modern LCDs, made for a much better typing experience.