The problem is that it can always be taken away from you. Remember, the Affordable Care Act ruling is supposed to come out this summer.
I am on an orphan drug myself (subcutaneous immunoglobulin, which I am self-infusing at the moment...) which costed $278,000/year under contract, when I lived in the US. Of course the provider bills a much higher amount. But the figure I gave is the one that is paid out, over the course of a year.
You should know that the third leading cause of death in the US is believed to be preventable medical errors. This has been corroborated via multiple follow-up studies, just google "third leading cause of death US medical errors". But, here is the original article: https://www.bmj.com/content/353/bmj.i2139
You can go to the "best hospitals", have the "best insurance", and "be able to pay for care", but you cannot evade a statistic like that. The medical error rate is on par with developing countries, by the way.
Also, 7-8% of the general population collectively has some sort of rare disease, which is theoretically treated by orphan drugs. There are now orphan drugs that cost $2 million/year per person, and the cost is so extortionate that it is literally going to screw over the US health system. Such meds have to be taken for life.: https://www.nytimes.com/2019/08/25/health/drug-prices-rare-d...
Also, life expectancy does not look so good in the US.
How healthy will we be in 2040? http://www.healthdata.org/news-release/how-healthy-will-we-b...
US was 43rd worldwide in life expectancy in 2016. In 2040, we are expected to be 64th.
Honestly, this kind of stuff is why I emigrated and I am a dual US|EU (Croatian) citizen. As an EU citizen, I have Freedom of Movement rights to live/work/retire in 30+ countries within the EU and EFTA (minus Liechtenstein--has an immigration quota).
Because of your health status, Canada, Australia, and New Zealand are off limits because they have strict medical inadmissability clauses in their immigration laws. I would stay away from the UK too, because they could implement such rules post-Brexit.
But, I have studied healthcare systems, logistics of healthcare, along with rules for acquiring citizenship, for hundreds of hours. If you want any help or advice, feel free to shoot me an email (check my profile).