"instantaneously" in the sense of first having to read the first byte to know how many bytes to read. So it's a two-step process. Given the current maximum length and SIMD, detecting the end-byte of my scheme is easily parallelizable for up to 4 bytes, which conveniently goes to 24 bits, enough for all current unicode code points, so there is no waiting for termination. Furthermore, to decode a UTF-8 characters needs bits extraction and shifting of all bytes, so there is no practical gain of not looking at every byte. It actually makes the decoding loop more complex.

Also, the human readability sounds fishy. Humans are really bad at decoding high-order bits. For example can you tell the length of a UTF-8 sequence that would begin with 0xEC at a glance? With my scheme, either the high bit is not set (0x7F or less), which is easy to see you only need to compare the first digit to 7. Or the high bit is set and the high nibble is less than 0xC, meaning there is another byte, also easy to see, you compare the first digit to C.

The quote also implicitly mis-characterized the fact that in my scheme an incorrect character would also not be decoded if interrupted since it would lack the terminating flag (No byte > 0xC0).