The most recent set of rules for the ACA contained two major new individual mandate exemptions:
1) People can claim a hardship exemption if all affordable plans cover abortion
2) People can claim a hardship exemption if their county of residence only has a single insurer.
All of this is only relevant for 2018 as the mandate penalty zeroes out on 1/1/19.
I am not sure how big of a deal this is in terms of how many people would drop coverage this year with these two new exemptions that they otherwise would have kept. The individual mandate penalty this year is 2.5% of income or $695 for a single adult, which ever is greater. There is a current hardship exemption for people who would need to pay more than 8.05% of their income for the least expensive Metal plan.
A good chunk of the country has to earn over $70,000 a year for a single 40 year old to not qualify for that mandate exemption. A family of three has to earn well over 600% Federal Poverty Level in a lot of Healthcare.gov states to not qualify for a hardship exemption.
Intuitively, a lot of people have an out from the ACA if they wanted to take it already. This makes me lean towards thinking that these two exemptions are primarily messaging rules and not rules with significant pragmatic impact.