I really like these thoughts, Markus!
I want to point out, however, that they may get at a somewhat different issue from this rule as originally worded. Your focus seems to be on voting/influence/participation for a population/culture/industry. The rule as originally worded talks about legal jurisdictions. Both issues are important.
The legal jurisdiction matters because we imagine scenarios where subpoenas or regulations could have the potential to impact Sovrin. We don't want any particular legal system or government to be able to do that disproportionately. In that perspective, Liechtenstein's legal system and India's legal system are qualitative and quantitative peers, and must be so; otherwise a legal change in India's stance on privacy, for example, could have a disproportionate effect on the network vis-a-vis Liechtenstein's. This jurisdictional requirement probably manifests in the proportion of validators, mostly.
The culture/population/industry proportional representation also matters, for matters of fairness and skew. Suppose 75% of the validator nodes come from universities. They're balanced or safe in terms of which legal jurisdiction they come from, but they're not balanced by industry; too many are from education. This would allow academia--the mindset, the tech stacks, the priorities--to have undue influence within Sovrin. Substitute other subsets, based on culture or population, for my university example, and you get all the other issues you are raising.
It seems less clear to me what the proper answers are to your questions, Markus. I'm not proposing any. I'm just saying that they don't invalidate the legal issue. The good news, I think, is that we don't quite have the same complexity that a government does, because we can assert many requirements and then be constrained by all of them, without reconciling them:
- We can't have too many validators in a single legal jurisdiction, regardless of how "big" the jurisdiction is. This can't be proportional.
- We ALSO can't have too many validators in a single industry vertical or a single culture or a single timezone or a single X, but perhaps "too many" is slightly more complex to analyze.