I have no idea what the legality of it would be, but it probably wouldn't make sense to accept or keep someone with an expensive-to-treat condition in small poo

I have no idea what the legality of it would be, but it probably wouldn't make sense to accept or keep someone with an expensive-to-treat condition in small pool like that because there may not be enough other members to absorb the cost. The whole point is that everybody has coverage under a high deductible standard insurance plan (which will be significantly cheaper than a low deductible plan), and then the group shares the risk of the deductibles. Best case, everybody pays less for insurance (including what they pay into the p2p pool). Worst case, someone gets sick and busts the pool (and gets kicked out if it's chronic), but everybody still probably paid less overall. Not sure how well this works if the person who got booted can't get their deductible reduced. I think health insurance is weird in a number of ways for this. It'd probably be great for e.g. homeowners insurance.