It does seems like an artifact that after-tax premiums aren't always deductible. We already have a model for how to do that in the homeowner's mortgage interest

It does seems like an artifact that after-tax premiums aren't always deductible. We already have a model for how to do that in the homeowner's mortgage interest deduction: insurers (banks) report the total of your premiums (mortgage interest) to the IRS, you get to deduct that value from your AGI. If you're paying for insurance with after-tax dollars, you can deduct it as long as you're a) itemizing, and b) have total medical + premium expenses >7.5% of AGI, but given that people who pay for insurance with pre-tax dollars get that benefit regardless of those criteria, it seems like it'd only be sane to relax the rules so that people paying with post-tax dollars get the same break.