I mean these things seem very different? AES is "just" a bunch of mathematical operations done on 16 byte chunks, you can make instructions which optimize that

I mean these things seem very different? AES is "just" a bunch of mathematical operations done on 16 byte chunks, you can make instructions which optimize that fairly easily. JSON is mainly a parsing problem, which .. is much harder to do in hardware. Hardware acceleration shines when you can do operations on large chunks of data at once. SSE/AVX/NEON/RVV are all general sets of vector operations, which can be used to optimize certain parts of parsing, as simdjson does. If there could be instructions added to further optimize JSON parsing, I have a feeling that they would be new general purpose vector instructions rather than anything JSON-specific. Or do you have any JSON-specific instructions in mind which would help beyond what the existing vector instructions already do?