The beauty is that twentix is only the beginning. It is the concept that can be applied to many particular uses. For the examples you brought up -- I could absolutely see a copy of twentix launched by people who don't think bitcoin cash and ripple should weigh in the valuation. The principle of an index can satisfy both with two different applications.
I appreciate how twentix keeps in bch because it removes my personal bias against projects I do not like. That is the idea of passive investing after all.