Dependent child over 18, I have supported all year and has lived with me 8 months of this year. Have ECN number for 2017 but not this year. Denied marketplace as she does not make enough and state has denied health coverage. If I file her (as she has no income) I get hit with penalty. If they have dropped the penalty then I can file an amended tax. Have read yes and no on this issue and I see no update on Turbotax.
It has been a situation of yes, it's valid, no it's not, yes it is. The ACA was the law for all of 2016. After the executive order a workaround was available for persons who decided they did not want to include the information. There was no guarantee, that the IRS would not still come after them. Now the effort to repeal has failed. Basically, the ACA is still the law.
If you choose to take your dependent, you will be penalized if they were not covered. You would need to see whcih works out better tax-wise, leaving them off or including them.