It's an interesting idea, but I think we're overlooking the human behavior aspect. These people don't necessarily act rationally, so a logical solution might not be the best one. I imagine they prefer to align with what is widely used by others, as it allows them to promote it at them. In your example, rather than creating their own chain, they might simply adopt whichever option has the highest usage among regular testnet users. This would sooner or later lead to a cat-and-mouse situation.