[mdp2021]

There exists a whole discipline in political science and mathematics about optimality in decisional workflows. So: you advance the discipline as a priority, then you reform states.

> The fairest [would be] obviously to allow voting for everyone

Certainly not, you are playing on a shade of meaning of "obvious" (i.e. "apparent"): that is strongly unfair to the gifted, cultivated etc. - it is unfair in terms of merit. And it is unfair to those who want an optimal system at their residence, etc.