v4 was 32-bit, v6 was 128-bit. I think that 64 bits is a more obvious happy medium.
Conveniently, 2^13 = 8192 allows you to use most of the information available in four decimal digits. And 64 = 13•5 - 1 means that you get a roughly even division into five address tiers (with either the first or last one half the size). 4095.8191.8191.8191.8191 is a bit worse than 255.255.255.255 but not nearly as bad as ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff.
Conveniently, 2^13 = 8192 allows you to use most of the information available in four decimal digits. And 64 = 13•5 - 1 means that you get a roughly even division into five address tiers (with either the first or last one half the size). 4095.8191.8191.8191.8191 is a bit worse than 255.255.255.255 but not nearly as bad as ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff.