I've built some programmable instrumentation before and to tell if something is a read you can just check the the opcode. You simply cover most common instructions and read the Mod R/M, but if you wanted it to work on more exotic instructions a fast disassembler would be easier.

I think I had this problem when working in ReversingLabs, and we had to write our own debugger for Windows... Yeah, this hardware breakpoint stuff was even a bit difficult, and only 4 available registers for having them. Memory protection is a quick hack, but it's page size.

Interesting, thanks for sharing! I forgot about your magazine, need to look into it more often