Perhaps I have misunderstood, but as I understand it a single-payer system only means that medical expenses are paid (and rate somewhat set by) a single entity, usually the government (similar Taiwan's national health insurance); or it can be a system where the services are provided directly by the single-payer (closer to the UK NHS).
However, I am not aware of a single payer system where drug/treatment/equipment production and R&D decisions have also been centralized to the single payer.
In fact, the company that article references as the kind that might not be profitable/investable long term (Gilead Sciences) has 3 locations in the UK, 2 in Canada, and 1 in Taiwan. Likely indicating that they either do business or hope to do business in those single pay systems.
Thus even a single payer system would not prevent the companies controlling R&D from declining to bring such treatments to market for a single payer system to purchase. No if the means of R&D, production, and distribution were also controlled by the single payer . . . but that begins to look an awful lot like socialism of communism.
Even today CRISPR is out there and when the patents expire someone will produce treatments using it (if they are viable). Maybe it will be a rival, perhaps it will be a biotech startup, or perhaps it will be a state university medical school using grant money from NIH, heck maybe Amazon/Apple/Musk-himself will further back a play in healthcare. If your are a major drug company maybe you can sit on a treatment for disorder A so that you can sell medication for it, but if your rivals start curing disorders B/C/D which you also sell drugs to manage you are eventually going to have to join in.
Of course an established investment firm used to investing in drug companies would worry about a paradigm change. So perhaps this should be in the same file as clickbait articles, no one has a use for personal computers/the internet, or online retail will destroy the economy in its entirety.
As an alternative, albeit all too rosy for capitalism, CRISPR gene editing becomes a common place mechanism for treating genetic conditions. The patents, if any, that limit the use of CRISPR expire and every Tom/Dick/Harry biotech startup, medical school research program, or individual who can read ATGC AUGC can choose to focus on ID'ing the genes associated with various illnesses and the versions of the gene not associated. All treatable by swapping in the non-illness gene into the same delivery mechanism. The FDA develops more expertise, if not expedience, in approving these treatment. Reusing the same mechanism and simpler approval result in greatly lowered development of approval costs, allowing profitability at lower and lower levels of sales. This allows more and more obscure disorders to be treated, while prices fall from the $1,000 a pill ($84,000 for a course of treatment) for hepatitis C today. Investments, the market, and large firms adapt to this shifting model and money flows into companies that not only develop that will have customers for long periods of time, but those that demonstrate their R&D can consistently develop new approvable gene treatments.