It's not nationalization though; all the insurance companies are still private or publicly-traded companies, not entities under government control. Medicaid is nationalized insurance, but Medicaid is not the only insurer that falls under the regulations set forth in the ACA, and it doesn't represent all Obamacare sign-ups. If Obamacare took all the private insurance companies and said, "you are now operated by the Federal Government," yes, that's nationalization.
Maybe you will have better luck than I did.