I think RISC would actually be far easier, since there are far fewer irregular instructions (like you get with x86) and you could leverage the fixed instruction size to not have to worry about some things.
Honestly a low LOC Assembler is a bit of a :shrug: for me, since the compilation of assembly from a higher level language is where things are ridiculously complex, assemblers are basically just translation mappers, there are some weird things that happen in them, but the vast majority of weirdness is covered elsewhere. It is a neat experiment to write an assembler certainly, but I found it much more interesting in Uni trying to express complex high level concepts in assembly. I came to appreciate just how ridiculously helpful compilers are.
Honestly a low LOC Assembler is a bit of a :shrug: for me, since the compilation of assembly from a higher level language is where things are ridiculously complex, assemblers are basically just translation mappers, there are some weird things that happen in them, but the vast majority of weirdness is covered elsewhere. It is a neat experiment to write an assembler certainly, but I found it much more interesting in Uni trying to express complex high level concepts in assembly. I came to appreciate just how ridiculously helpful compilers are.