As I said, the network/providers would be local to Mass because there is no reason an Ohio company can't contract with providers in Mass for their newly-enrolled Mass members at reimbursement rates commensurate with what is needed to get them on board as providers but still make a profit relative to what they charge their Mass members for premium. Either by "renting" an existing Mass plan's network or working directly with Mass providers to establish their own network. The main thing that prevents that now is existing law and the fact that Mass lawmakers don't want us to have that choice because it would undermine their nannyism.
Just as a multi-state property company charges different rents in Bumblefuck, Ohio and Boston, Mass, a multi-state insurance company could charge rates based on the local costs. But, without all the extra crap Mass forces, the rate would still be much lower than what I have to pay now for insurance in Mass. My auto insurance company isn't based in Mass, but they contract with many service providers in Mass to service their Mass members. They probably pay them more than is needed in other states, but Mass members also pay more for insurance. The same model could work for medical insurance.
Yes, it would be much smarter for Mass lawmakers to get rid of all that shit they require, but they're never going to.
Because there would be a small pool of MA policyholders for an Ohio company, your premiums would be so high that you would generally be better to self-insure. You can NOT escape the numbers. Insurance functions by spreading financial risk among a LARGE number of policyholders. The smaller the number of policies in a network the higher the risk. Further you can not pool MA policyholders with policyholders elsewhere because the medical costs are not the same between the areas. people in one place and people in a distant place are different. They have different lifestyles, different risks, and different base medical costs. By even trying you end up with massive increases for most policyholders, i.e. what has happened under the ACA. It is in no way "fair" to ask people in bumblefuck to pay extra just because some other fool likes living in Manhattan.