There don’t seem to be many advantages to words larger that 64 IMO (they do exist, but things like GMP exist for that). If the purpose would be parallel processing (a la SIMD), we already have “256 bit x86” with AVX2. IIRC, Intel’s x86 chips can process 256 bits of integer data at the same time. And if you want 512 bits, AVX-512 exists as well (but it’s implemented internally as two sequences of 256 bit data)

> 256 bit

but, why? do we need more than 16 exabytes of memory?

Right. Does anyone even need a megabyte? As Bill Gates famously (didn’t) say, “640k ought to be enough for anybody”.

Joking aside, we very well may one day have more memory available that 64 address lines can handle. RISC-V’s spec does have a stub chapter for “RV128”