Would think that timeline is more likely to be extended than shortened. There will be successor missions, and other space use cases for which derivatives of an astronaut transfer vehicle have value.
The bigger question will be whether it's better for Boeing to take the relatively low cost option of fixing the propulsion system which to some extent is their third party supplier's issue, in a funding environment where operating actual missions is more favourably funded than R&D, or whether that's sunk cost fallacy when SpaceX is clearly ahead of them.
It probably won't be extended, but there isn't no reason for people to think otherwise. It has been extended in the past, and NASA's own white paper from this year says that extension is a possibility if there are no commercial LEO stations suitable to NASA by 2030 and if Russia agrees to continue their participation. This is despite the contract for the Deorbit Vehicle already being awarded to SpaceX; it would simply wait until later.
> there isn't no reason for people to think otherwise
It’s possible, not probable.
It would take an act of the Congress to keep the ISS funded. There is zero indication that status quo will change nor a strong constituency for changing it.
This basically. Either there's a functional commercial replacement which is theoretically also a use case for a properly functioning Starliner or the ISS gets extended. Plausibly both. It doesn't have a fixed life limit, hasn't stopped working, hasn't stopped being used for experiments, and a commercial space boom era when microgravity experiments started turning into businesses would be a weird time for the US to decide it was a waste of money and give the space station monopoly to China...
The ISS may not, but Starliner does have a fixed life. It is meant to fly on the Atlas V, which is end-of-life. Once those are gone Starliner would need to be integrated and recertified to fly on a new rocket, probably Vulcan, but it's doubtful Boeing would want to spend the money to do this.
In response to your other point, I am very skeptical of microgravity experiments becoming a big industry. I think NASA (as an organization, I'm not talking about individuals in NASA) is mostly interested in continuing human space flight simply because it keeps the public interested in space, which makes NASA's funding more secure.
The bigger question will be whether it's better for Boeing to take the relatively low cost option of fixing the propulsion system which to some extent is their third party supplier's issue, in a funding environment where operating actual missions is more favourably funded than R&D, or whether that's sunk cost fallacy when SpaceX is clearly ahead of them.