This is a pretty decent protocol. I've used it to add support for debugging a C64 application via VICE in my 6502 assembler MOS. [0]
The last time I did a deep dive into the protocol it was missing a few features like viewing memory (or, rather, I think it was in the protocol but not really useable in VS Code yet?) but it is a well thought-out protocol overall.
The only drawback is that the communication protocol is different from the one used by LSP, it would've been nice if this had been identical.