If the tax credit based on comprehensive coverage was $1000/month, and catastrophic coverage cost $400/month, would someone who chooses to only have catastrophic still receive the $1000/month (giving them $600/month they could use on anything regardless of whether or not it is related to healthcare), or just receive $400/month, or receive whatever their insurance and medical costs actually are each month up to $1000/month?

If the later two it would be universal healthcare. Not sure how the first would be classified.

High deductible health plans are a thing, and fulfill the current (weak) insurance requirement in the US so the last half of that is here today.

I’d wager that a lot of people using HDHPs are doing so in order to be allowed to use HSAs as a stealth (but best) additional retirement account.

https://www.madfientist.com/ultimate-retirement-account/