Not so much a disruption, but splitting these huge homes into duplexes is an easy ticket. HOAs and neighborhoods will fight it because "there goes the neighborhood"

The design of many of these doesn't really lend themselves into being split into duplexes.

Zoning laws or local regulations (not just HOA) most likely would prevent it. An example is in Seattle some of the most expensive neighborhoods have strict rules that prevent multi-tenancy housing and the people living there actively fight to preserve that.

Does that stop share houses? If so how?

This is already being done. I read an article about it a few months ago. It's like living in a dorm. There's a shared kitchen and bathroom, but you have a private bedroom. I don't remember the term for it. ("Shared Living" seems to be about people with disabilities, but it was a name similar to that.)

I do not wish to live in that kind of complete nightmare. And there is no such thing as too big house. How can someone even come up with that. I encourage that person to move into 10m^2 room and live there for like 8 years or so.

10m^2 is probably too small for many people, but that doesn’t mean there isn’t some inflection point where the marginal cost of upkeep outweighs the marginal utility of additional space. As an absurd example, would you want to live in a house the size of Montana, and be responsible for all of the maintenance, or would you prefer something more human-scale, like a 40-bedroom mansion?

Size of Montana would be too big :-) But anything with at least 100m^2 would do, below that would be way too small for normal living