Possible development to support three wordlists at once?

[undeath]

There is no hashcat-native way of doing combinator3 with rules. A simple solution would be creating an intermediate wordlist with a space appended to each line, then creating a second intermediate wordlist containing the result of combining the first intermediate one with itself (as said before, with a 13mb wordlist this is infeasible) and then using the second one in a normal combination attack with the original one.

A slightly more technical solution would be modifying the combinator3 source code to fit your needs and pipe that to hashcat.