This is the terminal equivalent of one of those games that go for "pixel art aesthetics", but as soon as something scales or rotates it's clear everything is a billboard texture being blitted to a high-res surface and the pixels are just rectangles that look low-res. Terminal apps aren't an aesthetic, they are intended to provide as clear an affordance as possible within a certain set of constraints. In React web apps, those constraints are not there, so why should the aesthetics be? A React component that reintroduced those constraints, for example representing the screen as a grid of characters+attributes and rendering those to the DOM, might be interesting, but this is just copping a "look" to show your friends on r/itsaunixsystem and I'm not sure what the practical appeal is.

The AS/400 bit is neat, though. Very reminiscent of ISPF, the equivalent interface on System/360 and System/370 mainframe systems. Those UIs evoke everything we Gen-Xers and younger associate with the boring, awful dinosaur days of computing but... with a bit of training, data entry clerks, customer service reps, cashiers and the like could become very efficient with them.