I disagree with the claim that learning x86 assembly is not useful. I occasionally use inline assembly in my day job. It's very rare, but it does happen. If you're doing C or C++, it helps to know a little bit of x86 assembly when debugging. There are also certain optimizations that you often need inline assembly for, such as using the built-in Intel instruction for CRC32 calculations.

I learned Z80 assembly when writing software for the TI-85. But if I were giving advice to someone interested in learning assembly now, I would suggest learning x86... it's more useful, and just as fun.