[astrodust]

There's so few characters for which this would work reliably that it's basically pointless, plus it would require two or three actions to create a single character, further slowing down your typing.

Some typewriters do have accents as characters you can overtype, but these are simple to add by comparison, they land in consistent places. Chinese characters are anything but consistent.

Example: https://en.wikipedia.org/wiki/Dead_key

[zokier]

The introduction section of Ming Kwai typewriter patent is interesting reading (in addition to the classic beautiful drawings): https://www.google.com/patents/US2613795

The concept looks like it should be applicable to computer keyboards, and especially virtual touchscreen ones. Heck, I'm half-curious to prototype such myself just to see how it works.

[astrodust]

That thing looks impressively if not fiendishly complicated.

That seems like it's not an overtyping system, but one of selecting a single character based on a series of keystrokes.