This reminds me of a news story I saw on a major television network many years ago, maybe 15 to 20 years ago, about wealthy seniors who use Medicare, which they were fully entitled to. From what I recall, they were trying to get across the point that these seniors could afford to pay for their own healthcare and shouldn't be entitled to use Medicare. But the law is what matters, and they are entitled. There is no "should" or "shouldn't" in that sense as those are just opinions. All these years later, nothing has changed.
My opinion is that saving should not be disincentivized, which is what happens if you factor in existing wealth for a benefit or entitlement. Savings rates are low enough as it is.
I like rantk81's example, and is the very thing I was thinking of when I read the OP. You have two identical earners, one lives frugally and saves throughout his career building a nice nest egg, and the other one is a fool who spends like a drunken sailor having a great time with nothing saved. Rewarding the fool while penalizing the frugal saver is a terrible idea. The ACA's method of using income to determine Medicaid and subsidy eligibility makes the most sense, which explains why that's what is actually specified in the law, despite some complaints among a minority of the public.
As to the question in the subject, my answer is a resounding, "No! I am not concerned about that at all." If you note, the article linked to is over 2 years old, and so is this one
https://www.cnbc.com/2016/01/27/theyre-millionaires-and-they-get-obamacare-subsidies.html . These days, there are definitely concerns about the ACA that are frequently discussed, especially with the sabotage by the Trump administration (and the removal of the individual mandate in the tax cut law), but this particular issue discussed in this thread is way down the list of what concerns the vast majority of people. I can't remember it even coming up in any mainstream article recently. Just like Medicare and that news story from many years ago, I don't expect anything to change for the wealthy individuals who want to take advantage of the law as it is written, and think it is very unlikely there will be an asset test for ACA in the foreseeable future (Medicaid or subsidies.)
For me personally, when I FIRE in about a year, I expect to still have over $1.2M in addition to my fully paid-for residence, and I will take full advantage of ACA subsidies and CSR's as best I can as legally entitled to under the law. "Shoulds", "shouldn'ts", "designed for" and opinions in general are not a factor. This will allow me to spend upwards of $30K/yr on my travel budget. :)
You are seriously talking about outliers here. A person with a couple of mil would be more likely.
Areed. In the article I linked to, the author mentioned clients with up to $3M. I don't fit any of the 3 people in the example. The third person is close in income, but I'm single and plan to regulate my taxable income to about $18K/yr while not working at all, and I have $1.2M invested, which isn't specified for the third person, but I certainly don't have $50M as the second person!