""It would be different pools under different rules," said one senior health policy source..."

Literally the definition of how every other type of insurance works. You select the coverage you determine you need based on your own calculated risk of possible but unlikely events you cannot (or do not want to) realistically save to cover, and are pooled with other similarly situated persons (based on the insurer's actuarial data) to pay costs directly related to the calculated risk they take that you or a significant number of fellow poolees might actually need to use the plan.  If you want broader coverage, you are free to pay for more.