There's cost in the CPU because - Every register must be usable as a pointer, so if you make your addresses (i.e. pointers) too big for no good reason you're w

There's cost in the CPU because - Every register must be usable as a pointer, so if you make your addresses (i.e. pointers) too big for no good reason you're wasting silicon. - A solution to the above is picking a subset of registers that can address memory and making them big and leaving others as is, but this complicates the architecture and makes it ugly and complex - Another solution is to alias names so that registers are accessible either as monolithic 128/512/1024 blobs or as smaller subslices (A32_1 is the least significant 32 bits of the 128-bit register A, A32_2 is the next 32 bit slice and so on). This lessens the waste because when you don't need a 128-bit register you have 4 32 bit register instead and there's no such thing as too many registers. x86 does something vaguely similar but it's super ugly for different reasons, I don't see any problems with an architecture designed like this from the start, someone better at Computer Architecture might. - All functional units in the CPU will have to be the size of the largest register N, this would be a waste if they don't have the ability to function instead as N/n parallel n-bit units instead, and designing this into the architecture might be complex and entailing a lot of decisions. (e.g. If a 128-bit adder is functioning as parallel 4 32-bit adders, where do the 4 separate overflow bits go?)