Even though it defies the definition of insurance, exemplifies socialism, and is a huge driver of high insurance premiums (as it should be), Republicans are unlikely to brave the political heat required to remove Obamacare's "guaranteed issue" provision which functionally forces health insurers to cover pre-existing medical conditions.
As it stands today, you can be uninsured, learn you have a disease, buy "insurance", and saddle the rest of the insured population with your medical costs. It's like allowing someone to buy car insurance after an accident or homeowners insurance while the roof is on fire. As a business model, it is insane. As public policy it's only less insane to the degree that you can fool voters into thinking that the costs of the policy are minimal and that insurance companies are evil and deserve whatever happens to them. Sadly, it's all to easy to fool voters.
So, like all "free" goodies, guaranteed issue popular with voters who see things as free when they're simply paid for by others.