`BitSlice` or a sound way to implement one

Yeah, it's an interesting idea for a greenfield language (and maybe greenfield CPU). Treating bits as non-independent parts of a byte doesn't really feel different to me from treating bytes as non-independent parts of a word, and that was definitely a thing for a long time. And 64-bit address spaces are BIG, dividing the maximum size by 8 isn't really a problem. I guess that might be a downside for smaller address spaces, that you either need two kinds of pointers or a relatively low max memory limit to fit that extra addressing in.